Stress and Stressors Research Paper

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Stress is what we experience through a complex interplay between external forces in the environment (stressors) and our perceived ability to adapt to them. Although often viewed as harmful, stress is a normal adaptive response that helps us deal with life’s difficulties and prepare for action. Not all stress is bad, and in many cases it is necessary to perform optimally. This chapter provides a general overview of how stress is defined, its effects on psychological and biological processes, ways to measure different types of stress, and how stress is affected by cultural experiences. This chapter is closely related to other chapters on coping (how people deal with stress) and health psychology because stress is one of many psychological factors that can influence the incidence or progression of disease.

Stress can arise from external or internal sources, conflict, harm, loss, challenge, or frustration. Prolonged or chronic stress can have detrimental effects on a person’s psychological and mental health, but important individual differences exist that may make a person more vulnerable or sensitive to external sources of stress. Psychological and physiological changes that accompany stress are measurable and are related to various outcomes. Because of the significant impact stress can have on our lives, researchers are interested in finding ways to manage stress effectively and glean the benefits it provides while minimizing its harmful effects.


According to Richard Lazarus (1999), early models of psychological stress adopted analogies from engineering and physics. Robert Hooke, a 17th-century physicist-biologist, discussed how external force (load) applied to a particular area of a structure (stress) creates deformation (strain) of that structure. Over time, the use of the terms stress and strain came to apply to models of psychological stress, where the stress stimulus (or stressor) is the external force and the stress response is the body’s reaction to the stressor. Historically, researchers have focused mainly on the stressors, the physiological response to the stressors, or more recently, the complex interaction between them and how cognitive factors such as appraisal affect this relationship.

In the first approach, stress is viewed in terms of the external events to which we must adapt. These stimuli could be anything ranging from catastrophic events that affect large numbers of people (natural disasters, terrorist acts), to the major life events of an individual (marriage, unemployment), to the daily hassles of life (traffic, shopping). The second way stress has been defined is in terms of the response to these events. In this case, there is no prediction about what kind of stimulus could be a stressor because virtually any stimulus could be. Rather, the focus is on physiological changes that occur, such as changes in heart rate or stress hormone levels. However, one major problem of this definition is being able to distinguish an increase in heart rate due to psychological stress from an increase due to exercise. In this model, both would be considered stressful.

Limiting the definition of stress to either the stimulus or the response fails to take into account the relationship between them and the individual differences that mediate this relationship. As proposed in a third definition of stress by Lazarus and Folkman (1984), “Psychological stress is a particular relationship between the person and the environment that is appraised by the person as taxing or exceeding his or her resources and endangering his or her well-being” (p. 19). Much like bacteria or a virus (stimulus) interacting with the immune system (response) to affect the incidence or course of illness, there is a complex interaction among events in the environment, how we perceive those events, and the resources we have to deal with them in determining the amount of stress we experience. It was in this context that individual differences in responses to environmental stressors became apparent. For example, people who are exposed to the same event, such as a loss of employment, may react very differently, possibly becoming depressed or perceiving it as an opportunity to obtain a better job.

Cognitive appraisal refers to the mediating thought processes that determine how we will respond to the stressor. Hearing a fire alarm when we know it is a fire drill will not likely be interpreted as dangerous, while a fire alarm without that knowledge could be frightening. Our initial appraisal of the alarm as dangerous depends on our resources available to cope or deal with it, but that is not the end of the appraisal process.

Appraisal may be categorized as primary or secondary, depending on when it occurs. Primary appraisals are relatively immediate in the face of stressors, but evaluation also occurs later during secondary appraisal. Primary appraisals can be further categorized. One type of primary appraisal is “irrelevant,” in which the stimulus is likely to be of no consequence—for example, hearing about a decline in the stock market when we have no stock investments or learning that a Hollywood couple has broken up when we have no interest in either partner. Another type of primary appraisal is “benign-positive,” where we perceive the event as either maintaining or promoting our well-being, such as receiving notice that a cancer treatment has been effective or that our car has been successfully repaired. The third type of primary appraisal is the “stress” appraisal, in which we are threatened by a loss or harm, such as the loss of a loved one or the possibility of doing poorly on an exam. Finally, we may appraise the event as “challenging,” such as having an opportunity for a promotion at work or the opportunity to compete in an athletic event. These primary appraisals are not mutually exclusive; you could perceive something to be both challenging and threatening. Appraisals of threat and harm tend to lead to negative emotions such as depression and anxiety, while challenge appraisals result in more positive emotional outcomes.

Based on different appraisals of the event, Lazarus (1999) categorized psychological stress into three types. The first is “harm/loss,” in which a person deals with the effects of harm or loss that has already taken place such as financial loss or loss of a loved one. The second is “threat,” which is perceived loss or harm that has not occurred yet, but may occur in the future, such as the threat of doing poorly in school or a close relationship coming to an end. The third is “challenge,” which occurs when a person feels that although there may be difficulties in accomplishing the task, he or she can still be successful with effort and persistence.

When appraising a situation as harmful, a secondary appraisal is performed to assess how well equipped we are to deal with it. The nature of the secondary appraisal depends on what coping responses are available to us and our belief in how successful we can be in overcoming the situation. It is during this secondary appraisal that feelings of helplessness may develop if a person feels no control over managing the situation. Generally speaking, situations that are appraised as harmful and outside of our control are the most stressful, particularly if the stakes are high.

Rotter (1966) developed a survey to measure people’s internal and external attributions of control. When we perceive that relatively permanent personality traits such as intelligence or shyness can account for success or failure, then we have an internal locus of control. An external locus of control attributes successes or failures to luck, chance, fate, or powerful others. Although it depends on the situation, greater stress occurs when a person feels less control. In this case, it may result in learned helplessness, but as noted above, appraisal is not a one-time event. As people begin coping with the stress, appraisal continues to occur interactively with the environment as they decide how effective their coping is and if coping resources have changed.

The relational model of stress proposed by Lazarus and Folkman (1984) can be compared to a seesaw. On one end of the seesaw are the demands or environmental load that arises from perceived threat, harm, or challenge. On the other end is the amount of resources available to deal with it. When they are in balance, we experience low or moderate stress. If the resources are equal to or exceed the current demands, we may experience boredom, but if the demands exceed our resources, we experience stress that at extreme levels can result in trauma, hopelessness, panic, and depression.

Factors Related To Appraisal


Kurt Lewin (1935) proposed that there are three types of goal-oriented conflicts that affect our decision making. Subsequently, these conflicts may create situations noted by Lazarus that we appraise as threatening, harmful, or challenging. These conflicts emerge from the combination of environmental forces that elicit approach behavior toward goals with positive valence or withdrawal/avoidance behavior away from goals with negative valence. Of course, if one of the conflicting choices is of much greater value than the other, the conflict situation will not create much stress. Conflict arises primarily when the choices are between roughly equivalent positive or negative outcomes and when the person is strongly motivated to make a decision.

Lewin’s first type of conflict results from the competition of two goals that we view positively and desire to approach, but both cannot be obtained at the same time (approach-approach conflict). For example, a person may be faced with the choice to pursue a college education or forego college to play professional basketball. On a smaller scale, the decision might be which of two groups of friends to hang out with on a Saturday night. Both goals are desirable, but the choice of one will likely exclude the opportunity to reach the other, at least for a time.

The second type of conflict arises when pursuit of a single goal will have both favorable and unfavorable consequences (approach-avoidance conflict). For example, going to the dentist to have a cavity filled is desirable to prevent further dental problems but at the same time could be painful. Or, a student may want to try out for a high school musical, but fears that it will elicit teasing from peers or that he or she may not get the desired part. If repeated attempts at achieving the goal are blocked, frustration may result and the person will withdraw from further attempts.

The third type of conflict, avoidance-avoidance, occurs when we are forced to choose between two undesirable actions. This situation might occur if a parent threatens a child with punishment unless the garbage is taken out. The act of taking out the garbage and the looming punishment are both unpleasant alternatives, so in this case the choice is between the “lesser of two evils.” Unfortunately, another potential outcome of avoidance-avoidance conflict is hopelessness, in which the person may experience despair or, alternatively, increased stubbornness and inflexibility.

Predictability and Controllability

Predictability refers to how likely an event will occur given certain information; controllability is how much control an organism has over the event. Both are important factors in determining the stressfulness of an event.

Jay Weiss (1972) conducted studies on rats to determine the role of predictability and control in the development of stress-related illness. In previous studies employing physical stressors such as forced swimming, the illness that followed the stressful situation could be due to the psychological stress associated with fear, anxiety, helplessness, or the physical stress from excessive muscle fatigue. Thus, to separate the effects of psychological stress from physical stress, he devised a way to keep the physical stress constant across experimental conditions, but vary the amount of psychological stress by manipulating the amount of control over receiving electrical shock.

In a typical experiment, Weiss would have three rats in identical experimental chambers. One rat served as the control and did not receive any shocks. Two other rats were assigned to a “yoked” procedure in which each rat received the same number, timing, and intensity of shocks. However, there was an important difference between the experiences of these two yoked rats. In one experiment, one of the rats received a warning signal that shock was forthcoming (high predictability), while the other rat received the same warning signal at random intervals (no predictability). Rats in the unpredictable shock condition developed greater stomach ulcerations than did the rats that received predictable shock, which had fewer ulcerations compared to the control group. Because each yoked rat had identical physical stress from the shock, but had different amounts of psychological stress based on the level of predictability, Weiss concluded that it was the predictability that accounted for the difference in stomach ulcerations.

In subsequent experiments, Weiss varied the controllability of shock rather than the predictability of shock. In a similar procedure to his predictability experiment, he arranged the experiment so one member of the yoked pair of rats could terminate or avoid the shock if it performed a particular behavior when the warning signal appeared. Its partner received a shock only when the first rat failed to escape or avoid in time. Thus, although they all received the same shocks, the second rat of the yoked pair was helpless in escaping or avoiding the shocks. In several of these studies, the helpless rats lost more weight and had greater stomach ulcerations, indicating greater psychological stress.

From these experiments, Weiss (1972) concluded that one of the most important factors in the development of stress is the type and amount of feedback we get from our coping responses. Behavior that results in a change in the stressful situation will reduce stress, while behaviors that are ineffective will maintain or increase the stress, illustrating the importance of coping behaviors in response to stress, which are further addressed in other chapters.

Physiology Of Stress

General Adaptation Syndrome

Initially, Hans Selye (1976) was not interested in studying the stress response. In pursuit of isolating a new hormone, he injected various tissue extracts into rats. Regardless of the type of extract, all the rats ended up with enlarged adrenal glands, atrophy of the thymus gland (an important gland for the development of immune cells), and ulceration of the stomach lining. These results led him to describe a nonspecific physiological pattern of responses to physical injury or biological stress caused by toxins, mechanical damage, or virtually any noxious substance. He defined stress as “the nonspecific response of the body to any demand” (p. 1). His pioneering work on stress in the 1930s and thereafter resulted in his being acknowledged as the “father of stress research.”

Selye’s enduring contribution to stress research is the classic model of how the body responds to stress over time. In the general adaptation syndrome (GAS), the body first responds to a stressful event very quickly, in what he called the alarm stage. The rapid response is primarily due to increased sympathetic nervous system activity, which is responsible for the “fight-or-flight” reaction. If the stress continues, the person enters the resistance stage, during which the body accommodates or adapts to the initial stressor. During this phase, increased cortisol is released from the adrenal gland. Cortisol has many effects on the body, including increasing blood pressure and increasing the availability of glucose in the blood stream. However, these stores are limited and under longer periods of stress they will eventually become depleted. The chronic release of cortisol can have inhibitory effects on the immune system, resulting in increased susceptibility to disease or illness. Thus, the third phase of the GAS is the exhaustion stage, in which the body can no longer withstand the stress; consequently, the person may become sick or even die.

Selye’s focus on the stress response led him to differentiate between distress (bad stress) and eustress (good stress). Both types of stress appeared to have similar nonspecific effects on the body, although distress resulted in greater disease over time. However, this distinction remains controversial and later research has not adequately supported this distinction. Some of this confusion may have arisen from prior work by Yerkes and Dodson (1908), who suggested that performance improves with increased arousal, at least to a certain point. With further increases in arousal, performance begins to deteriorate. Although this relation between arousal and performance is generally true, there were large differences in how people responded to the same situation. Part of the variability in responses depended on the easiness of the task, while another part could be attributed to individual psychological differences. For example, two different basketball players faced with a game-winning free throw could either perceive it as an opportunity, a challenge, or a terribly threatening situation in which they could “choke” and be faced with a loss.

The Autonomic Nervous System

The autonomic nervous system (ANS) is prepared to respond quickly to stressful situations by promoting rapid, adaptive physiological responses. Often referred to as the “fight-or-flight” response, it is descriptive of how the body prepares for action, which includes widening of the pupils for increased vision, dilation of breathing passages for increased oxygen consumption, increased heart rate and blood pressure to increase blood flow, and hormonal changes including release of adrenaline and cortisol. These responses are normally adaptive in situations that call for action, such as running away from a bully at school or competing in an athletic event. However, the autonomic nervous system is also activated in response to harmless events such as taking a test or giving a public speech.

The HPA Axis

Besides autonomic nervous system activation, a second major response to stress is the release of glucocorticoids (primarily cortisol) from the adrenal gland. When the brain perceives a threatening situation, the hypothalamus releases corticotrophin-releasing hormone (CRH), which initiates the release of adrenocorticotropin hormone (ACTH) from the anterior pituitary, causing the adrenal cortex to release cortisol. Cortisol mobilizes stored glucose from the liver and muscles to increase blood glucose levels for use by the brain and muscles. It also increases blood pressure and has a complex host of effects on the immune system. Initially, it may promote brief activation of immune cells. However, in the long run it severely suppresses immune function. Experiments using physiological or psychological stressors later suggested that the HPA axis, a complex set of connections and interactions among the hypothalamus, the pituitary gland, and the adrenal gland, was more likely to be activated in cases of threat or harm, but not so much with physical stressors such as exercise, fasting, and heat (Lazarus, 1999).

Homeostasis, Allostasis, And Allostatic Load

Walter Cannon (1929), a physiologist, described how the body closely regulates physiological variables such as glucose levels, temperature, and salt around a “set point,” which is a narrow range of ideal values. Fluctuations outside of the range of these variables trigger compensatory mechanisms to restore the body to the set point. The process of maintaining the body within such a narrow range is known as homeostasis or steady state. Homeostasis is disrupted by physical stressors such as cold, fasting, or decreased oxygen, but psychological stressors can also initiate similar responses.

In his book Why Zebras Don’t Get Ulcers, Robert Sapolsky (2004) suggested that any shift away from homeostasis creates stress. Thus, when a stressor causes a shift from homeostatic balance, such as a decrease in ideal body temperature, then the body compensates by triggering warming mechanisms to restore body temperature within the normal range.

Bruce McEwen (1998) has extended the theory of homeostasis to recognize the fact that an optimal range of blood pressure or glucose can vary depending on the situation. McEwen defines “allostasis” as the adaptation of the body to multiple shifts from homeostasis. Thus, although homeostasis is a tendency to maintain a steady state, in reality, the optimal range depends on the situation. For example, a stressful situation may temporarily call for increased blood glucose levels and stress hormone release that would normally be considered out of the ideal range. Over time, allostatic systems may begin to wear out if they are frequently activated or if they are not properly turned off at the end of the stress period. In such cases, the body begins to suffer the consequences of “allostatic load,” which ultimately can lead to disease or injury to the brain and body, as later noted.

In a brief review article, Sapolsky (1996) described how activation of the HPA axis by stress can have damaging effects on the brain. Glucocorticoids, such as cortisol, are released by the adrenal gland and enter the bloodstream, where they can travel to the brain and attach to glucocorticoid receptors found in high concentration in the hippocampus, a structure important for learning and memory. High levels of glucocorticoids in the brain from either chronic stress or external administration can significantly affect the hippocampus, leading to impaired memory in both animals and humans. In animals, a few days of chronic stress are sufficient to make neurons in the hippocampus more susceptible to death from stroke or lack of oxygen. A few months of stress cause a reduction in the size of specialized branches of hippocampal neurons, and eventually neuronal death.

Sapolsky (1996) also mentioned that, until recently, human studies were unclear about how stress affected the brain, but with improved brain-imaging techniques and better-designed studies some data suggest that high cortisol levels associated with depression, post-traumatic stress disorder (PTSD), or metabolic diseases may decrease the volume of the hippocampus by 12 to 15 percent. These changes may be permanent, as noted by the fact that formerly depressed participants still had smaller-than-normal hippocampi even though they had recovered from their depression. An alternative explanation is that individuals with smaller hippocampi may be predisposed to depression or PTSD symptoms. Another problem with glucocorticoids affecting the hippocampus is that the hippocampus is part of a negative feedback loop that normally dampens high cortisol levels. Thus, damage to the hippocampus may interfere with the body’s ability to limit or decrease the cortisol response when needed.

Creating And Measuring Stress

Two major types of stressors are those that are short-lived (acute) and those that persist for longer periods of time (chronic). A second distinction is between physical stressors, which are due to changes in nutrition, body temperature, oxygen level, or injury, and psychological stressors, which originate from events such as academic examinations, changes in employment, mortgages, troubled relationships, or moving to a new location. Psychological stressors (or even the anticipation of the stressors) can activate the same physiological systems as physical stressors.

Life Events

When stress is defined in terms of environmental changes that produce stress, specific major life events can be identified and ranked according to perceived stressful-ness. One such list of major life events is the Holmes and Rahe’s (1967) Social Readjustment Rating Scale. After generating a list of potential major life events that could force a person to make at least some kind of adjustment, these events were rated according to whether the event would require more or less adjustment than marriage (accounting for both the intensity and duration of adjustment required). Of the 43 life events, the top three events rated as most stressful were death of spouse, divorce, and marital separation, while the least stressful were vacation, Christmas, and minor violations of the law. This scale does not distinguish desirable (outstanding personal achievement) from undesirable (trouble with the boss) events—both are considered stressful. However, this survey was published 30 years ago, and life events common to our culture have changed over this time. For example, compared to 1967, having a “mortgage over $10,000” would be much less stressful today than back then.

A more recent and student-friendly life event scale developed by Renner and Macklin (1998) is the College Undergraduate Stress Scale (CUSS), which assesses life events that are particularly relevant for college students. To create the scale, Renner and Macklin first had participants generate a list of potential stressors they face in college. Then, a second group of students rated these items in terms of how stressful they would be. The final list of 51 items includes life events such as rape (#1), writing a term paper, falling asleep in class, as well as positive events such as going on a first date and getting straight A’s. As with the LES, the CUSS does not distinguish between desirable and undesirable events.

Daily Hassles

Besides major life events, we may face day-to-day hassles such as caring for children, maintaining health, deadlines at work, preparing meals, and managing investments. Anita Delongis and her colleagues (1988) developed a survey called the Daily Hassle and Uplifts Scale to assess these events and others that could be considered a hassle (annoying or bothersome) or an uplift (joyful or good). Most of these events may not cause a lot of stress on their own, even if they are a hassle, but Delongis and others (1982) found that the cumulative effects of daily hassles predicted physical symptoms of illness better than major life events alone. Unfortunately, the potential benefits of daily uplifts didn’t seem to offset the negative effects of the daily hassles.

Acute Stress

Laboratory Stress

In addition to naturally occurring life events, standardized procedures in the laboratory can also be used to promote stress. In animal studies, stress has been induced by placing rats in a cold environment or forcing them to swim with no way to escape. Other common methods to create stress in animals are the use of physical restraint, sometimes in conjunction with exposure to bright lights or loud noises for several hours at a time, or the creation of a conditioned fear by pairing a stimulus such as a tone or light with shock. When the conditioned stimulus is presented alone, fear is usually measured by an interruption of other behaviors when the animal “freezes” or stops moving. In the natural environment, freezing makes it less likely that rats will be noticed by a predator.

Milder forms of stress are apparent in tasks that measure anxiety or fear in novel situations. For example, in an open field test a rat’s anxiety is indicated by how cautiously it explores a new environment. The dependent measure is often the number of squares of a virtual or real grid it crosses in a specified period of time. Similarly, the elevated plus maze measures exploratory behavior in a novel, somewhat fearful setting. A rat or mouse is placed on a plus-shaped maze that is several feet above the floor. Two of the four arms of the maze have no walls, while the other two arms have high walls for “safety.” As with the open-field test, less exploration of the maze area (particularly the open arms) indicates greater anxiety.

Physical stressors such as cold, restraint, and shock are not the only way to induce stress in animals. Another prominent source of stress is social stress. Separation of infant animals from their mothers is stressful for both the mother and offspring. Species from mice to nonhuman primates that form social dominance hierarchies also experience stress from introduction of a new member of the species into the social group (humans too!).

Acute stress in humans is easily induced in the laboratory. Although there are greater ethical restrictions when using humans, there are several proven acceptable ways to create stress, most of which are created by variations in the social situation. In studies of stress and cardiovascular or immune function, participants often undergo a mental arithmetic task or speaking task, both of which are performed in the presence of others on short notice. In the arithmetic task, the participant may be asked to subtract 13 from a four-digit number, and continue to subtract 13 from the resulting numbers while the experimenter (and others) watch and suggest that they go increasingly faster.

Another stressful task that includes mental arithmetic is the Trier Social Stress Test (TSST). Developed by Kirschbaum and others (1993), participants rest for 30 minutes after a catheter is placed in their arm for later blood withdrawal and analysis. Then they are taken into another room where there is a video camera, tape recorder, and three persons seated at a table. The participant is told to assume the role of a job applicant who is undergoing a personal interview with the three “managers” seated at the table and to prepare a speech to convince the panel that he or she is the right person for the job. The experimenter states that the participant’s speech will be video- and audiotaped, analyzed for nonverbal behavior, and rated on a performance scale. The participants are then taken to the original room, where they have 10 minutes to prepare for the 5-minute speech. Following the speech, participants are asked to perform mental arithmetic similar to that described above for another 5 minutes. This social stress task typically results in a two- to fourfold increase in salivary cortisol levels that start to rise at the beginning of the speech and peak about 10 minutes after the end, but continue to remain elevated for as long as 60 minutes afterward. Heart rate also increases dramatically by about 25 beats per minute, but returns to normal more rapidly.

The TSST produced endocrine and autonomic responses in a large majority of participants, but personality traits did not seem to affect the magnitude or pattern of responses (Kirschbaum et al., 1993). However, men tended to have a greater cortisol response than women did, and smokers had a decreased hormone response compared to nonsmokers. The component of the TSST that most likely triggers the stress response is the perceived evaluation of performance by others. This type of stress can also arise when a person is undergoing a real job interview or taking an academic examination.

Academic Examinations

Academic examinations have long provided another naturalistic setting to study stress. It is estimated that about 16 percent of prospective college students experience a high level of anxiety that can start to interfere with their performance on a test (Zeidner & Nevo, 1992). Test anxiety scales, such as the Test Anxiety Inventory (Spielberger, Gonzalez, Taylor, Algaze, & Anton, 1978) assess how much people worry about their performance on a test and the impact of doing poorly on a test. It also measures the emotional (physiological) reactions that accompany test taking, such as a racing heart or sweaty hands. Generally speaking, performance on a test decreases as test anxiety increases. Poor performance on an exam could result in greater test anxiety, creating a downward spiral of performance. When considering using academic exams as a stressor, there are important methodological and statistical considerations, which have been reported elsewhere (Stowell, 2003).

Chronic Stress

There is no distinct time frame to distinguish short-term from long-term stress, but any stressor that is not adequately handled will continue to require mental and physical resources, which may lead to Selye’s GAS stage of exhaustion. Although acute stress can promote readiness of the body for action, effects of chronic stress are potentially deadly.


In 1979, a nuclear reactor at Three Mile Island in Pennsylvania nearly had a complete meltdown, creating panic and fear as people fled the area amidst warnings of a nuclear explosion. Those people who continued to live in the area were under the constant fear of exposure to radioactivity, creating a condition of chronic stress. McKinnon and others (1989) studied some of these individuals, who had, on average, lower immune cell numbers than a control group that lived farther away from the area. Natural disasters can also produce long-term stress, as demonstrated with Hurricane Andrew, the Northridge, California, earthquake, and more recently, Hurricane Katrina.

Although not a natural disaster, the terrorist acts of 9/11 had disastrous effects on people living in New York and in other parts of the country. In a national survey of adults conducted three to five days after 9/11, 44 percent of respondents were experiencing one or more substantial stress symptoms, suggesting that even people not directly exposed to the event were affected by hearing about it or seeing the media coverage (Schuster et al., 2001).


In addition to disasters, chronic stress can also arise from changes in employment, social relationships, or financial condition. One well-accepted model of chronic stress is the burden of providing long-term care for someone with Alzheimer’s disease or other forms of dementia. Learning, memory, and cognitive function progressively decline in these patients, sometimes even to the point that the patient may no longer recognize his or her spouse. Many Alzheimer’s patients require constant care for years before they die. From the time of diagnosis, about half of the patients live for another seven to eight years, which creates a tremendous amount of strain on the caregiver who watches a loved one continue to deteriorate. Caregiving also makes it difficult to establish or continue supportive social relationships outside of the home and may create changes in employment or financial status.

Janice Kiecolt-Glaser and her colleagues (1991) studied the effects of caregiving on stress and immune function and found that caregivers were more depressed and had poorer immune function than a control group of people with similar age, sex, and martial status. The effect of chronic stress on the immune system also likely accounted for why caregivers were also less likely to produce a sufficient number of antibodies to protect them against the flu virus after receiving a flu vaccination (Kiecolt-Glaser, Glaser, Gravenstein, Malarkey, & Sheridan, 1996).


Although being married is associated with greater overall happiness and well-being compared to being single or divorced, it can also be a significant source of chronic stress. Studies by Kiecolt-Glaser and others (1996) suggest that even a 30-minute marital disagreement can have significant effects on stress hormone levels and immune function. In several studies, both newlywed and elderly couples discussed one or two areas of disagreement in their marriage for 30 minutes while they were being videotaped, so their verbal and nonverbal behavior could be studied. A nurse periodically drew blood from the couple’s arms before, during, and after the conflict to measure stress hormone levels and immune cell function. This discussion resulted in significant changes in both measures.

More recently, Kiecolt-Glaser and colleagues (2005) repeated this marital study with an additional dependent measure of immune function: wound healing. Couples who expressed greater hostility during their interactions were slower to heal standardized wounds, which were eight suction blisters on the nondominant forearm. Couples identified as high in hostility healed at 60 percent of the rate of the other couples who were identified as low in hostility. Whether married or not, that little dispute over money, doing the dishes, or what TV program to watch can possibly have major effects on a person’s health over time.


Post-Traumatic Stress Disorder

Understanding how the body responds to stress is crucially important in stress-related illnesses. For example, PTSD develops as a result of exposure to a traumatic event, whether it is a car accident, rape, war, or natural disaster. The hallmark symptoms of PTSD are avoidance of feared stimuli, exaggerated startle, and spontaneous reminders of the event such as flashbacks. Individual differences are important to consider because people exposed to the same event may differ in the appearance of PTSD symptoms.

Understanding the neurocircuitry of fear and the factors that may protect one from developing PTSD symptoms is important. Pavi and colleagues (2007) confirmed that the right hippocampus of PTSD victims is smaller than the right hippocampus of people without PTSD. However, this correlational finding could mean that having PTSD caused a reduction in the volume of hippocampus due to neuronal shrinkage or cell death, or that a small hippocampus may predispose someone to develop symptoms of PTSD. Alternately, perhaps a third variable could account for why they vary together. New research using brain imaging has found support for the second explanation. Gilbertson and others (2002) found that the hippocampal volumes of identical twins were similar to each other, even when one member of the twin pair had PTSD and the other did not. Thus, having a smaller hippocampus was probably not the result of getting PTSD, but was more likely a predisposing factor. Results from brain-imaging studies will not be able to indicate precisely who will get PTSD, but they might tell us who would be more susceptible to PTSD and how to reduce the risk.

Acculturative Stress

Increased globalization of economic, social, political, and cultural factors has also increased the pressure to adapt to changes that result from their interdependency. John Berry (2006) presented a model for how ethnocultural groups adapt to living among other cultures, a process that he termed “acculturation.”

In a simple model where two different cultures have direct contact with each other, it is important to understand how the cultures differ prior to contact with each other, the type of contact they have with each other when they meet, and how the two cultures adapt to each other or in some way become a mix of cultures. Thus, at the culture/group level, there are cultural changes that have subsequent psychological effects on individuals of the culture, which may result in “acculturative stress.” Berry (2006) suggested that the amount of stress experienced through the acculturation process depends on the type of strategy employed by each culture that is brought together.

Four acculturative strategies may be categorized along two dimensions. The first dimension is the relative amount of maintenance of existing culture and identity, and the second dimension is the relative amount of interest in developing relationships among the different culture groups. Focusing on the perspective of the nondominant group, integration is seeking to maintain their own cultural identity while seeking increased relationships with the other groups. Maintaining cultural identity but withdrawing from contact with others is termed separation. Placing less value on holding on to cultural beliefs (or having little possibility of maintaining cultural beliefs) but seeking increased interaction with other groups is called assimilation (much like the “melting pot” analogy) while seeking decreased interaction is marginalization. This last strategy is most often associated with poor psychological adjustment. Of course, the dominant culture group also plays a large role in the selection of acculturative strategies.

In accordance with the stress, appraisal, and coping model of Lazarus and Folkman (1984), Berry (2006) suggested that the greatest stress results when there is little control over events associated with acculturation (especially for the nondominant group), such as intergroup conflict or pressure to conform. Integration is likely to be the least stressful; marginalization is likely to be the most stressful. Assimilation and separation strategies lie in the middle of the continuum. Psychological stress may also result from changes in economic conditions upon first arrival in a new culture and difference in marital adaptation. For example, a husband may develop intercultural relations at work while his wife may be isolated at home or have only limited interaction with a few others who share her culture. Generally speaking, psychological stress increases initially upon contact with other groups but then declines over time. However, depending on the acculturation strategy, acculturative stress may be chronic, resulting in depression, low self-esteem, and difficulty in interacting with other groups.

Future Directions

New stressors are becoming apparent as society and technology change. Although the broad categories of stressors have not changed considerably, there are new specific types of stressors. For example, “technology stress” may originate from playing intense video games, getting stuck on a slow Internet connection, or having to learn a new software program. Future research will continue to identify the relevant stressors of our time and how to effectively deal with them.

The basic physiology of stress is well known, but there is much to learn about the brain in terms of how individual differences play a role in the appraisal and coping processes. A better understanding of the neurobiological events may lead to novel techniques in treating individuals who suffer from stress-related disorders. Genetic studies may also help identify individuals who are more susceptible to the effects of stress.


Much of the past research on stress has focused on the stressor itself or the body’s physiological reaction to the stressor. More recently, stress is viewed as the result of an interactive process that takes into account changes in the environment, personal resources available to deal with these changes, and our cognitive interpretation of other factors such as control and predictability.

Stress is unavoidable, but it prepares us for action by producing physiological changes that are normally considered adaptive, as described in Selye’s GAS. However, prolonged or repetitive stress can add wear and tear to the body (allostatic load), resulting in illness or disease. One major determining factor is the duration of the stress, with acute stress having relatively mild effects and chronic stress having more harmful effects.

Stress is likely to arise in situations where there is conflict between goals or when a person is experiencing a major life event, such as divorce or the death of a loved one. Natural disasters and other catastrophic events, including terrorism, can have detrimental effects on mental and physical health, particularly susceptibility to PTSD, depression, and decreased immune function. Even the daily hassles of life can build up to become a significant source of stress. Future research will continue to focus on the individual differences that promote a healthy response to the many stressors we face.


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