Why don't women have hairy chests?
Well, actually some women do.
As a culture, we are obsessed with becoming hairless. There are waxing salons, threading salons, laser hair removal treatments, electrolysis, and who could forget good ol' Nair? The truth is that as mammals we are designed to be covered in body hair. We have the same number of hair follicles as our hairier simian friends, but our hair is shorter and finer. The only truly hairless parts of the body are the umbilicus (belly button), the lips, the nipples, the palms, and the soles.
There are two types of hair on the body, vellus hair and terminal hair. Vellus hair is soft, fine, colorless, and short. Vellus hair helps the body maintain a steady temperature by providing some insulation. Terminal hair is found on the head, the armpits, and the pubic area, and on the face and chest in males. It is coarser, darker, and longer than vellus hair.
Hirsutism is the growth of long, coarse hair on the face and body of a woman in a pattern similar to men. Hirsutism can be the result of many medical conditions, including polycystic ovary syndrome, hormonal imbalance, tumors, thyroid disease, obesity, anorexia, or medications. Excess hair on the face or chest may simply be due to your genetics. Luckily, there are plenty of ways to get rid of excess hair.
Excerpt from: Why Do Men Fall Asleep After Sex?