Androgenic Alopecia - Age Effect

Age Effect

Androgens stimulate growth of facial hair, but can suppress scalp hair, a condition which has been called the 'androgen paradox'. The American Academy of Dermatology reports that in adult men, the incidence of androgenic alopecia is roughly equivalent to chronological age, with half of men experiencing hair loss by age 50.

A number of hormonal changes occur with aging:

1. Decrease in testosterone
2. Decrease in DHT and 5-alpha reductase
3. Decrease 3AAG, a peripheral marker of DHT metabolism,
4. Increase in SHBG.
5. Decrease in androgen receptors in the scalp with age.

This decrease in androgens, androgen receptors and the increase in SHBG are opposite the increase in androgenic alopecia with aging. This is not intuitive, as testosterone and its peripheral metabolite, DHT, accelerate hair loss, and SHBG is thought to be protective. The ratio of T/SHBG, DHT/SHBG decreases by as much as 80% by age 80, in numeric parallel to hair loss, and approximates the pharmacology of anti-androgens such as finasteride.

Free testosterone decreases in men by age 80 to levels double that of a woman at age 20. 30% of normal male testosterone level, the approximate level in females, is not enough to induce alopecia; 60%, closer to the amount found in elderly men, is sufficient. It has been theorized that the testicular secretion of testosterone "sets the stage" for androgenic alopecia as a multifactorial diathesis stress model, related to hormonal predisposition, environment and age. Supplementing eunuchs with testosterone during their 2nd decade, for example, causes slow progression of androgenic alopecia over many years, while testosterone late in life causes rapid hair loss within a month.

An example of premature age effect is Werner's syndrome, a condition of accelerated aging from low fidelity copying of mRNA. Affected children display premature androgenic alopecia.