Hair loss or baldness is a genetic trait—but unlike what you may have been told, it’s not necessarily passed down from your maternal grandfather. Medical science has come to learn that baldness genes are actually passed down from both sides of the family—and they affect hair loss in women as well as men. Baldness genes may also skip generations and are utterly random in terms of which siblings (male or female) they will affect. They may even have very different effects on siblings in the same family.
Hair loss in men
Androgenetic Alopecia, or "male pattern baldness," occurs in men whose hair follicles are sensitive to the hormone dihydrotestosterone, or DHT. Over time, DHT-sensitive hair (usually found on the top and front of the head) becomes weaker, finer, and eventually stops growing. However, even men who experience advanced baldness have healthy hair follicles around the sides of the head that last a lifetime. Even though these healthy hairs are exposed to DHT, they are resistant to this hormone and survive for a lifetime.
Hair loss in women
In women, hair loss usually begins at menopause. Before this time, DHT is counteracted by estrogen, but when estrogen levels drop, women’s hair follicles may also become prone to the effects of DHT. Unlike men, hair loss patterns in women are marked by thinning throughout the scalp; fully bald spots at the crown are rare.