A dermatologist explains why some men lose their hair

We asked a dermatologist to explain why some men go bald, and why it can happen in their 20s. According to Dr. Jennifer Chwalek, genetics will likely determine whether or not you lose your hair, and how soon it will happen. Testosterone is converted to dihydrotestosterone in the hair follicle by an enzyme called 5-alpha-reductase. When the enzyme attaches to the androgen receptor in the hair follicle in susceptible individuals, it causes the follicle to produce a smaller hair. According to Chwalek, about 40% of the population has some degree of thinning.