In many cases, women grow hair on their chins because they have high levels of androgens, according to MedlinePlus. Androgens are the hormones responsible for male sexual development and the development of male characteristics.
Both men and women produce androgens, but males typically produce more than females. Women produce these "male hormones" in their ovaries, fat cells and adrenal glands. Experts from the National Women's Health Resource Center say an excess of androgen is one of the most common hormonal disorders in women.
Some women with polycystic ovary syndrome also develop dark hair on their chins. Scientists do not know what causes PCOS, but some researchers believe it is linked to excessive amounts of insulin. It appears too much insulin promotes the production of androgens in women.
There are other causes of chin hair in women, but most of them affect hormone levels in one way or another. Tumors of the adrenal glands and ovaries affect androgen production, making it more likely a woman will have dark hairs on her chin. Some women have a condition called hyperthecosis. This condition causes the ovaries to produce excessive amounts of androgens.
The use of certain medications also influences hair growth on the chin, according to MedlinePlus. These medications include minoxidil, cyclosporine, testosterone, anabolic steroids, danazol and phenytoin.