Age & hormones, 2 factors that influence the hair cycle
How age influences the hair cycle
How hormones influence the hair cycle
Hair strands begin to change during puberty, when large amounts of male and female hormones arrive in the blood.
The hair growth cycle is determined by the influence of these hormones. The latter are produced by the endocrine gland and are transported in the blood. They then bond to target cells, in this case, the roots of the hair, which capture the hormone’s signal and react as a result.
There are 2 types of hormones: male or androgenic hormones, including testosterone, and female or estrogen hormones such as progesterone.
These hormones play a different role in the body and particularly in the hair cycle.
Female or estrogen hormones participate in hair growth by slowing down growth and prolonging the anagen phase.
Inversely, male or androgenic hormones accelerate the hair cycle. Strictly speaking, androgens alone do not trigger hair loss. This is in fact the result of a chemical reaction, DHT, which is triggered by the combination of androgens and (-alpha reductase, an enzyme found in the scalp. DHT accelerates the hair growth cycle to such an extent that the hair follicles become saturated and begin producing shorter and shorter hairs until they are worn out. They are then able to produce only a fine layer of “fuzz”, and then nothing at all. These inactive follicles retract into the dermis and the skin becomes smoother.
Men and women secrete male and female hormones, but in different quantities. Women also produce androgens but in quantities 20 times less than men.
This is why women never go bald, except in cases of disease or particular hormone disorders. However, they can experience increased hair loss or a modification in hair texture caused by a drop in female hormone production during menopause.
Pregnancy also influences the hair’s growth cycle. During the second or third trimester of pregnancy, a woman’s body secretes more female hormones, and 90% of the hair is in anagen phase. Women often lose a significant amount of hair after childbirth, (called post-partum hair loss), after estrogen levels return to normal and the “doping effect” on hair growth comes to an end.