INTRODUCTION
Biological organisms are continuously exposed to a myriad of internal and external stimuli and stressors. As a response to these stimuli, living organisms have developed natural defence and adaptation mechanisms over time.
Stress is a common stimulus and well-known causal factor of hair growth disorders and hair loss. The link between psycho-emotional stress and hair loss can be distinguished according to three levels of interaction.1
Interaction Level 1: Acute or Chronic Stress as a Primary Inducer of Telogen Effluvium
Telogen effluvium is one of the major hair growth disorders and is closely related to stress. Occurring mainly in women, telogen effluvium can be induced as a result of stress or extreme hormonal imbalance. This creates a disruption to the normal hair growth cycle in which anagen (growing) hairs prematurely enter the telogen (resting) phase. Consequently, symptoms begin to appear in the form of short, sudden bouts of hair shedding with little to no hair growth.2
Interaction Level 2: Acute or Chronic Stress as an Aggravating Factor in Hair Loss Disorders Whose Primary Pathogenesis is of Endocrine, Toxic, Metabolic, or Immunological Nature (eg, androgenetic alopecia, alopecia areata)
Androgenetic alopecia is the most common hair growth disorder in women and men. The large majority of hair growth disorders occur due to a change in the hair growth cycle, which is usually androgen dependent and genetically determined. In the case of androgenetic alopecia, testosterone is converted to dihydrotestosterone (DHT) via 5α-reductase. DHT then binds to androgen receptors in the hair follicle, which results in the shortening of the anagen phase and simultaneous prolongation of the telogen phase, combined with hair follicle miniaturisation. Symptoms of hair thinning and loss result from a gradual reduction in hair diameter and a visibly widened hair parting.3,4
Alopecia areata is an autoimmune disorder that affects men and women equally. It is thought that the development of alopecia areata may occur as a result of an environmental influence on the immune and hormonal microenvironments of the hair follicle. Representing approximately 0.7% to 3.8% of all patients attending dermatology clinics, alopecia areata is characterised by delimited patches of hair loss on the scalp. Hair loss symptoms in this connection can become more widespread, with complete loss of hair on the scalp; alopecia totalis, or by a complete loss of all hair on the scalp and body; alopecia universalis. Moreover, people with alopecia areata may experience a reduced expression of glucocorticoids due to weak response to acute physiological stressors.5.6
Interaction Level 3: Stress as a Secondary Problem in Response to Prior Hair Loss
Stress resulting as a consequence of hair loss, in contrast to being a primary inducer or aggravating factor, can lead to further perpetuation of hair loss. This may be due to a vicious cause-and-effect circle arising between stress-as-response and hair fall.7
Stress and the Hair Follicle
The role and function of the hair follicle is sophisticated. Through the continuous, cyclic production of hair fibres, the follicle serves as a sensory organ as well as an instrument of psychosocial communication and protection in humans. This is
