It is possible that early adversity could set in motion a detrimental developmental cascade. This includes changes in the hypothalamic-pituitary-adrenal (HPA) axis activity. This, in turn, influences self-regulation in childhood. Both patterns of high and low cortisol in the HPA axis are associated with impairments in executive function, which, in turn, is important for self-regulation.

Early adverse experiences are associated with problematic socio-emotional development. This may occur through alterations in neurobiological systems and impairments in self-regulation.

Children make great developments in self-regulation in the first years of life. Regulation success depends on the caregiver in infancy but afterwards, the child progresses to more internally-regulated behaviours. In toddlerhood, self-control, autonomy and compliance emerge as a function of increasing self-regulatory skills. Furthermore, the first years of life are characterized by maturational changes in the HPA axis. Both self-regulation and the HPA axis functioning can be disturbed by adversity.

Direct and contextual (i.e. indirect) adversities often co-occur. All forms of early adversity challenge the child’s coping resources, leading to chronic stress. The development of stress-response systems is affected by early adversity. Allostasis refers to the body’s ability to achieve stability through physiological changes in stress-mediating systems (e.g. secretion of inflammatory cytokines; changes in cortisol). This is adaptive in the short-term as they prepare an individual for a stressful event. However, prolonged exposure to stress (i.e. sustained allostatic state) leads to altered activity of stress mediators. This can eventually lead to allostatic overload, which is a major risk factor for pathology.

Activity of the HPA axis leads to cortisol increases when the organism is confronted with a stressor. Allostatic load could consist of heightened levels of cortisol. Chronic stress could also lead to a downregulation of the HPA axis to protect the body from damage caused by the toxic effects of stress hormones. It is believed that chronic stress initially elevates cortisol levels but this eventually becomes reduced compared to normal cortisol levels.

Caregivers provide a strong social regulator of HPA axis activity in the first years of life. Abuse refers to repeated exposures to threatening behaviours perpetrated toward the child. Neglect refers to lack of necessary care from the primary caregiver. There appears to be a pattern of hypoactive HPA axis activity in neglected children. Foster care may have a regulating influence on cortisol levels among children with maltreatment experiences. Foster children exhibited higher incidences of atypical cortisol patterns (i.e. both hypo- and hyperactive).

Hypoactivity of the HPA axis leads to low levels of cortisol in the morning. This, in turn, leads to flatter slopes of cortisol activity, which leads to a blunted pattern of HPA-axis activity. It is not clear whether abuse and neglect have differential effects on HPA axis activity. There is an association between maternal unresponsiveness and high cortisol levels in early childhood. It is possible that parental behaviour with the possibility of stress (e.g. maternal unresponsiveness) increases circulating levels of cortisol while neglect is severe enough to lead to downregulation of the HPA axis. This would imply that hyper- or hypo-activity of the HPA axis depends on the severity of maltreatment. However, there is no consensus regarding this.

There are contextual adversities which are not as extreme as maltreatment but could still influence typical development (e.g. poverty). Parental behaviour mediates the effects of contextual adversity on child outcomes. High-quality parenting is a powerful buffer against stress for children. Sensitive and responsive parenting may help children cope with stressful events and interactions that regularly occur in adverse contexts.

Elevated and low cortisol levels appear to be predicted by family instability. Inter-partner violence and socioeconomic status did not predict cortisol profiles. It is possible that different degrees of poverty differentially affect the child’s HPA axis functioning. Variations in the association between contextual adversity and HPA axis activity is probably related to other factors than chronic stress alone (e.g. parental behaviour).

There is no connection between specific types of early adversity and HPA-axis hyper- or hypoactivity in early childhood.

Changes in stress physiology (e.g. HPA axis) can impact many areas of a child’s life through the impact on the ability to self-regulate. Self-regulation refers to the ability to control emotions and behaviours. Self-regulation depends on executive functions. Adverse experiences are associated with deficits in self-regulation during childhood. Impaired self-regulation is detrimental as it contributes to behaviours that disrupt the child’s functioning (e.g. tantrums). Deficits in self-regulation can lead to behavioural problems during childhood and limiting opportunities to learn adaptive skills, increasing the risk for psychopathology.

It is thought that glucocorticoids as main actors of stress-response systems impact the development of brain structures and neural activity that underlie self-regulation. The prefrontal cortex supports effortful control, the ability to suppress a dominant response to perform a subdominant response. Impairments in the development of the prefrontal cortex could thus underlie deficits in self-regulation.

It is likely that contextual adversity exerts influence on the HPA axis through increasing experiences of direct adversity. The alterations in the HPA axis, in turn, impairs development and functioning of brain structures which are important for self-regulation. The impairment in self-regulation increases the risk for psychopathology in the long-term.

A blunted cortisol pattern is associated with lower effortful control. Hypocortisolism is a mediator between early adversity and attention and externalizing problems during kindergarten. High levels of cortisol may be problematic because of neurotoxic effects on brain structures underlying cognitive functions. Low levels of cortisol may be problematic because of it not being able to get enough metabolic resources necessary for optimal learning and memory consolidation. Besides that, basal cortisol levels are required for normal functioning of the sympathetic nervous system and the immune system.

Interventions that support parents to maintain high levels of responsiveness and warmth can be expected to improve the child’s regulation of stress physiology with cascading influences on self-regulation.