There are several causes of hirsutism ranging from high levels of androgens or male hormones in the blood to the side effects of medicines. The following are some of the reasons which can cause hirsutism.

Polycystic Ovarian Syndrome (PCOS)
PCOS is caused due to excessive production of androgens by the ovaries. It is a common cause of hirsutism and it is frequently (though not always) associated with irregular or absent ovulation and infertility.

Unexplained Hirsutism (idiopathic hirsutism)
For unknown reasons, some women have hair follicles that are abnormally sensitive to androgens. Androgen levels are normal and menstrual periods occur regularly in these patients. This tendency to develop hirsutism seems to be genetic, but the cause is not known.

Non-Classic Adrenal Hyperplasia
The most common abnormality of the adrenal glands that can result in hirsutism is a disorder called non-classic adrenal hyperplasia (NCAH). This condition causes the adrenal glands to overproduce androgens. The adrenals are small glands that sit on top of the kidneys and they play an important role in regulating hormone production. In women, they are the main source of androgen hormones.

HAIR-AN Syndrome (Hyperandrogenism, Insulin Resistance, Acanthosis Nigricans)
Some women are born with insulin resistance, a severe defect in the ability of insulin to control blood sugar levels. To compensate, the pancreas produces more insulin. Excessively high levels of insulin stimulate the ovaries to dramatically overproduce androgens This can lead to a variety of androgenic effects including hirsutism, scalp hair loss, acne, and irregular ovulation.

Cushing’s Syndrome
Cushing’s syndrome refers to over production of cortisol by the adrenal glands.
Although hirsutism may be seen in Cushing’s syndrome patients, it is not a primary feature of the disorder and there are several other symptoms with a greater impact on health that usually occur as a result of Cushing’s syndrome. Cushing’s syndrome is a serious, but rare disease.

Ovarian or Adrenal Tumors
On rare occasions, an androgen-producing tumor may develop in the ovaries or adrenal glands. This tumor may produce extremely high androgen levels. Symptoms, such as hirsutism or sclap hair loss, usually appear suddenly and progress quickly.

Menopause
Around the time of menopause, the ovaries stop producing estrogen, but they continue to produce androgens. Estrogens are antagonistic to androgens and restrain the effects of androgens on the body. The decreased levels of estrogen after menopause may allow the androgens to have a greater impact, leading to an increase in the number of dark terminal hairs, especially on the face.

Medication Side Effects

Drugs with characteristics of androgens may cause hirsutism. Anabolic steroids, used for increasing the muscle mass of chronically ill and debilitated people, and by some bodybuilders, are chemically related to androgens. Some older forms of birth control pill are also androgenic and can cause hirsutism. Some vasodilatory drugs used in heart diease can also cause hirsutism.