Hair is a keratinous strand of material that grows from follicles in your skin. Hair plays an important role on your body for sensory, protection and temperature regulation. Although most people grow hair on the head, armpits, arms, legs and groin, other areas of body hair stem from other factors. Many of these factors are biological, while others result from substances you place in your body.
Hormones known as androgens activate body hair growth. Androgens include common hormones such as testosterone. Although more common in men, androgens are also in women, produced in smaller amounts by the adrenal glands and ovaries. This makes body hair growth more common in men, but possible in women with hormonal imbalance, such as during a pregnancy or menopause.
Your genetics can also determine body hair growth, especially the Lhx2 gene, according to research by the Umeå University in Sweden. Genes decide when hair growth will occur, where hair growth will occur, and how sensitive your hair follicles are to the substances that activate hair growth. For example, a son may grow hair in similar quantities and areas as his father. A mother with genes that cause more prominent body hair growth may pass on the trait to her daughter.
Certain adrenal diseases may also affect the amount of hair that grows on the body. The adrenal glands produce androgens, which in greater quantity can cause an increase in body hair on both men and women. Adrenal diseases such as adrenal hyperplasia, Cushing's syndrome, and adrenal tumors can cause an imbalance in androgen production, leading to body hair growth.
Diseases affecting the ovaries can increase body hair growth in women. This is due to the role ovaries play in keeping hormone levels balanced in the body. Common ovarian diseases that can increase body hair include ovarian tumors and polycystic ovarian syndrome (PCOS). PCOS is one of the most common causes of abnormal body hair growth, according to the American Society for Reproductive Medicine.
Steroid medications introduce synthetic hormones into your body that can cause an imbalance in natural hormone levels. An imbalance toward androgens may cause an increase in body hair. Medications that can possibly cause this include danazol, testosterone, corticosteroids, metryrapone and anabolic steroids.