Early childhood is a critical period in a child's life that includes ages from birth to five years old.Poulsen, Marie K., and Karen M. Finello. "Foundations of Early Childhood Mental Health: Public Health & Life Course Perspectives." Preventive Medicine 583 Lecture. University of Southern California, Los Angeles. 25 Aug. 2011. Lecture. Psychological stress is an inevitable part of life. Human beings can experience stress from an early age. Although stress is a factor for the average human being, it can be a positive or negative molding aspect in a young child's life.

A certain amount of stress is normal and necessary for survival. A few stressors can be manageable for young children; stress can be beneficial by helping children develop skills needed to adapt to a new set of circumstances and deal with dangerous and intimidating situations. Some experts have theorized that there is a point where prolonged or excessive stress becomes harmful and can lead to serious health effects. When stress builds up in early childhood, neurobiological factors are affected. In turn, levels of the stress hormone cortisol exceed normal ranges. This theory however is based on animal studies and cross-sectional studies in humans, and the proposed impacts on brain centers have not been found in a landmark twin study and studies where neurobiological factors were measured in humans prior to stress or trauma exposure.

Researchers have proposed three distinct types of responses to stress in young children: positive, tolerable, and toxic. These labels are based on theorized differences in lasting physiological changes occurring as a result of the intensity and duration of the stress response.

Stress is caused by internal or external influences that disrupt an individual's normal state of well-being.Effects of Stress on the Body | Lachina. (n.d.). Retrieved April 9, 2018, from https://lachina.com/blog/effects-stress-body/ These influences are capable of affecting health by causing emotional distress and leading to a variety of physiological changes. Internal stressors include physiological conditions such as hunger, pain, illness or fatigue. Other internal sources of stress consist of shyness in a child, emotions, gender, age and intellectual capacity. Childhood trauma has lifelong impact.

Exposure to adverse childhood experiences can include separation from family, home violence, racial/ethnic disparities, income disparities, neighborhood violence, mental illness or substance use disorder of caregiver, physical/sexual abuse, neglect, divorce, a new home or school, illness and hospitalization, death of a loved one, poverty, natural disasters, and adults' negative discipline techniques (e.g. spanking). Additional external stressors include prenatal drug exposure, such as maternal methamphetamine use, other maternal and paternal substance abuse, maternal depression, posttraumatic stress and psychosis.

Levels of stress Researchers have proposed three different levels of stress seen in children during early childhood; positive, tolerable and toxic.

Positive stress is necessary and promotes resilience, or the ability to function competently under threat.Davies, Douglas. "Chapter 3: Risk and Protective Factors: The Child, The Family, and Community Contexts." Child Development, A Practitioner's Guide. 2nd ed. New York: Guilford Press. Print. Such stress arises from brief, mild to moderate stressful experiences, buffered by the presence of a caring adult who can help the child cope with the stressor. This type of stress causes minor physiological and hormonal changes to the young child; these changes include an increase in heart rate and a change in hormone cortisol levels. The first day of school, a family wedding or making new friends are all examples of positive stressors. Such experiences can promote healthy development within an environment of supportive relationships, giving children the chance to observe and practice healthy responses to stressful events.

Tolerable stress comes from adverse experiences that are more intense in nature but short-lived and can usually be overcome. The body's stress response is more intensely activated due to severe stressors. Some examples of tolerable stressors are family disruptions, accidents or a death of a loved one. It is important though to realize that such stressors are only tolerable when managed the correct way. Tolerable stress can turn into positive stress. With appropriate care from adults, young children can easily cope with tolerable stress and turn it into positive stress. However, if adult support is deficient in a child's coping stages, then tolerable stress can become detrimental.

Toxic stress can occur when experiences are long in duration and intensity. Children need caring and supportive adults to help them because it is difficult for children to handle this type of stress on their own. Therefore, the stress response may be activated from weeks to months or even years. Prolonged stress leads to adverse effects such as permanent emotional or developmental damage. If sufficient support is not available, this type of stress can result in permanent changes in brain development. Research has found that children experiencing severe and long-term abuse have smaller brain sizes. If the situation is not as severe, toxic stress will still alter the stress response system; these changes will cause children to react to a wider variety of stressors. However, with sufficient care and support from adults, children can return their stress levels to tolerable or good. Examples of toxic stress are abuse, neglect, violence and overall hardship without adult support. Toxic stress can have a cumulative effect on physical and mental health.

Allostatic load is "the wear and tear on the body" that accumulates as an individual is exposed to repeated or chronic stress. It represents the physiological consequences of chronic exposure to fluctuating or heightened neural or neuroendocrine response that results from repeated or chronic toxic stress. The term was coined by Bruce McEwen and E. Stellar in 1993.

Stages of stress Stress is encountered in four different stages in early childhood. In the first stage, stress usually causes alarm. Next, in the second or appraisal stage, the child attempts to find meaning from the event. Stage three consists of children seeking out coping strategies. Lastly, in stage four, children execute one or more of the coping strategies. However, children with lower tolerance for stressors are more susceptible to alarm and find a broader array of events to be stressful. These children often experience chronic or toxic stress.

Causes

In the US, non-white children from a lower socioeconomic status are more prone to exposure to adverse childhood experiences. Black children from a lower socioeconomic status in particular are most at risk for exposure to adverse childhood experiences. Socioeconomic status can be measured by education and income level. A chronic exposure to stress will lead to the decline of physical health and increase susceptibility to diseases.Fagundes, Christopher P., and Baldwin Way. "Early-Life Stress and Adult Inflammation." Current Directions in Psychological Science 23.4 (2014): n. pag. Web. 11 Sept. 2014. <http://cdp.sagepub.com/content/23/4/277.full>.

Situations that may promote stress in childhood include:Tennant, V. (2005). School of Education at Johns Hopkins University-The Powerful Impact of Stress. Johns Hopkins School of Education - Home. Retrieved February 2013, from http://education.jhu.edu/PD/newhorizons/strategies/ topics/Keeping%20Fit%20for%20Learning/stress.html.

Adoption Loss of caregiver attachment: Divorce/separation, foster care, parental incarceration Lack of attention Racism Separation from parents Exposure to violence: physical, mental and sexual abuse Substance abuse Being over-scheduled Feeling pressured to perform or behave beyond their ability Neglect: emotional and physical neglect Meeting new people Starting a new school Death of a loved one Illness: mental and physical Difficulty with school work Increased pressure/responsibility at home Being bullied

Stress and brain development Brain circuits and testosterone's systems are formed and activated in early life. These neurobiological systems of the body help maintain viability and are necessary for survival in early childhood and along the course of life.Gunnar, Megan, and Karina Quevedo. "The Neurobiology of Stress and Development."Advance (2007): 145–65. Annual Reviews. Web. 8 October 2011. <www.annualreviews.org>. When a child or adult experiences a stressor, the body will attempt to regulate the stress through releasing hormones that pass through the body. However, effects of the prolonged or frequent biological stress response may increase the risk for future physical and mental health problems in early childhood. Since brain circuits are vulnerable in early childhood, early stressors may impact the development of necessary brain connections. Therefore, the theory of toxic stress is that stress might alter or impair brain circuit formation and essentially result in a small brain size in young children. There are however no studies yet that have measured these brain circuits or volumes of brain centers prospectively in young children to prove this theory.

Stress response pathway in humans In humans, the stress response pathway consists of the sympathetic-adrenomedullary (SAM) system and the hypothalamic-pituitary-adrenal axis (HPA). The SAM system is a part of the sympathetic component of the autonomic nervous system. These systems are responsible for releasing epinephrine and norepinephrine (NE), also known as the flight or fight response hormones. When epinephrine is released it will bind to various receptors in various target organs; this will exhibit multiple roles in the fight or flight mechanism. The HPA system is responsible for producing glucocorticoids from the adrenal cortex; the main glucocorticoid in humans is the steroid hormone cortisol. In contrast to epinephrine, which takes a short amount of time for production, cortisol takes up to 25 minutes to reach peak levels. Also, cortisol is able to penetrate the brain through the blood–brain barrier, unlike epinephrine. Therefore, cortisol takes more time to form, but impacts the brain for a longer period of time. In conjunction, the SAM and HPA systems work to regulate stress and unite at the hypothalamus, which in turn regulates behavior.

Infancy, early childhood, and stress

When the body undergoes a stressful situation, the stress hormone cortisol is released. Cortisol helps the body prepare for stressful and dangerous situations. It gives a quick burst of energy, heightened memory and lower sensitivity to pain, among other things.Cortisol and Stress: How Cortisol Affects Your Body, and How To Stay Healthy in the Face of Stress. Stress and Stress Management - Causes, Symptoms, Stress Relief Tips and Stress Tests. Retrieved from http://stress.about.com/od/stresshealth/a/cortisol.htm. When cortisol is present in the body at high levels and for extended periods of time, however, the body's immune response may be suppressed. This leaves the developing bodies of children extremely vulnerable to damage and illness. Cortisol is usually bound to proteins in adults. The protein is called the corticosteroid-binding globulin (CBG). In newborn babies, CBGs remain low and increase during the first six months after birth. Therefore, as the amount of CBGs increase, more cortisol becomes bound to the CBGs. Due to this occurrence, plasma and total cortisol levels increase. Although there are low levels of cortisol at birth, the levels are sufficient to have serious physiological effects.