In dermatology, alopecia refers to accelerated hair loss. If alopecia is not slowed, it leads to partial baldness, or even a complete loss of hair.
Of all the forms of alopecia, the "androgenic" type is the most common (90% of alopecia cases). It may be early: at 20 years old, one in five men lose their hair, at 30 years old, one in three men, and at 50 years old, one in two men.
While androgenic alopecia is most common in males, it does affect 10-15% of women suffering from hair problems. This is linked to two main factors:
- Genetic background: a gene, which has not yet been isolated, is responsible for the fact that a person will have similar hair loss to that of their parents or grandparents.
- Male or androgen hormones: testosterone and DiHydroTestosterone (DHT). Testosterone circulating in the blood is transformed into DiHydroTestosterone under the influence of an enzyme: 5 alpha reductase.
In androgenic alopecia, enzyme 5 alpha reductase hyperactivity will lead to a shortened growth phase (anagen phase) for hair, and the miniaturisation of hair in the growth phase. The duration of each cycle will significantly decrease from an average of five years to several months. The 25 hair cycles will not last as long, which leads to thinning of the hair and gradually the complete disappearance of hair from large areas of the scalp: widow's peak, forehead and top of the skull.
Fortunately, however, hormone receptors of pilosebaceous follicles located on certain parts of the scalp are not sensitive to this 5 alpha reductase hyperactivity. This is the case with hair located on the neck and temples, which explains why bald men almost always retain a crown of hair.
For a hair transplant, it is precisely this privileged area of the scalp (donor area), where hairs will benefit for life from the normal course of their cycle, and will provide the hair to be transplanted to the area to be replenished (recipient area). Indeed, the transplanted hairs in the recipient area will continue to benefit from a normal rhythm in their cycle.
Other causes of hair loss
Seasonal loss: spring and autumn for four to six weeks. The sun affects the hormones responsible for hair growth. Hairs in the telogen phase are ejected by new hair.
Acute diffuse alopecia or telogen effluvium: following the events of high and prolonged fever, surgical shock, childbirth, acute deficiency, stress, serious accident or emotional psychological shock
Taking certain medications: anti-inflammatories, anti-hypertensives, anti-coagulants, anti-cancer medication, pills, cortisone or antibiotics
Pathologies: infections (fungal, bacterial, viral or parasitic), tumours (carcinomas, lymphomas), deficiencies (iron), burns or ionizing radiation
Scalp mistreatment: perms, straightening or curling products, braids and buns that are too tight
Alopecia: recurrent autoimmune disease