The relationship between cortisol, stress and psychiatric illness: New insights using hair analysis

• We discuss methodological issues in using hair cortisol concentration as a measure of long-term cortisol release.
• There is consistent evidence that effects of stress can be reliably detected using changes in hair cortisol.
• Results from studies measuring hair cortisol in specific psychiatric disorders are more variable.
• Results using hair may differ from those using other specimens such as saliva that measure short-term cortisol release.
• Assessments of cortisol levels using hair provides additional and complementary information to current methods.

BackgroundStress is an established important contributor to the development of mental illness and stress related disorders. The biology implicated in the homeostasis of pathological stress mechanisms is not fully established. One of the difficulties with current techniques is the limitation in capturing chronic levels of cortisol as an expression of stress levels in humans. Hair samples can be used to evaluate cortisol levels averaged over relatively long periods of time, therefore providing a more valid measure of chronic levels of this hormone. A highly replicable technique to measure long-term cortisol could prove pivotal in improving our understanding of the role of stress in psychiatric disorders.MethodsThis review synthesises all the published studies relating hair cortisol concentration (HCC) to stress and to psychiatric disorders. It describes and summarises their findings with the aim of providing a summary picture of the current state of this line of research.ResultsThe strongest finding to date is the replicable increases in hair cortisol associated with stressful life events. Findings in psychiatric disorders are more sparse and inconsistent. There is some support for the presence of raised HCC in major depressive disorders, and for lowered HCC in posttraumatic stress disorder, suggesting chronic hypercortisolaemia and hypocortisolaemia respectively.ConclusionsHCC is a promising methodology to study chronic cortisol levels with the potential to help characterise psychiatric and stress related disorders. The combination of chronic and acute cortisol measurements has the potential for more accurately determining different aspects of the stress response, and ultimately for the development of a biological marker to aid diagnosis and response to treatment.