What causes hair loss?

A number of things can cause excessive hair loss. For example, about 3 or 4 months after an illness or a major surgery, you may suddenly lose a large amount of hair. This hair loss is related to the stress of the illness and is temporary.

Hormonal problems may cause hair loss. If your thyroid gland is overactive or underactive, your hair may fall out. This hair loss usually can be helped by treatment thyroid disease. Hair loss may occur if male or female hormones, known as androgens and estrogens, are out of balance. Correcting the hormone imbalance may stop your hair loss.

Many women notice hair loss about 3 months after they've had a baby. This loss is also related to hormones. During pregnancy, high levels of certain hormones cause the body to keep hair that would normally fall out. When the hormones return to pre-pregnancy levels, that hair falls out and the normal cycle of growth and loss starts again.

Some medicines can cause hair loss. This type of hair loss improves when you stop taking the medicine. Medicines that can cause hair loss include blood thinners (also called anticoagulants), medicines used for gout, medicines used in chemotherapy to treat cancer, vitamin A (if too much is taken), birth control pills and antidepressants.

Certain infections can cause hair loss. Fungal infections of the scalp can cause hair loss in children. The infection is easily treated with antifungal medicines.

Finally, hair loss may occur as part of an underlying disease, such as lupus or diabetes. Since hair loss may be an early sign of a disease, it is important to find the cause so that it can be treated.


Alopecia (al-o-pe'sh-ah) is the technical term for any abnormal form of loss of hair. The natural falling out of the hair should not be confused with alopecia. When hair has grown to its full length, it comes out by itself and is replaced by a new hair. The natural shedding of hair occurs most frequently in spring and fall. On the other hand, hair lost in alopecia does not come back unless special treatments are given to encourage hair growth. Certain hairstyles such as ponytail and tight braids may be contributing factors in constant hair loss or baldness. Alopecia senilis (se-nil'is) is the form of baldness occurring in old age. This loss of hair is permanent. Alopecia prematura (pre-mah-tu'-rah) is the form of baldness beginning any time before middle-age with a slow thinning process. This condition is caused by the first hairs falling out and being replaced by weaker ones. Alopecia areata (ar-e-a'tah) is the sudden falling out of hair in round patches or baldness in spots, sometimes caused by anemia, scarlet fever, typhoid fever or syphilis. Affected areas are slightly depressed, smooth and very pale, due to a decreased blood supply. Patches may be round or irregular in shape and they may vary in size from one-half inch to 2-3 inches in diameter. In most conditions of alopecia areata, the nervous system has been subjected to some injury. Since the flow of blood is influenced by the nervous system, the affected area is also poorly nourished.