doctors do not know why certain hair follicles are programmed to have a shorter growth period than others. although a person's level of androgens -- male hormones normally produced by both men and women -- is believed to be a factor hair loss has nothing to do with virility. an individual's genes however -- from both male and female parents -- unquestionably influence that person's predisposition to male or female pattern baldness. telogen effluvium is temporary hair loss that can occur within a few months after a high fever a severe illness or extreme stress and in women following childbirth. drugs that can cause temporary hair loss include chemotherapy drugs used in cancer treatment blood thinners retinoids used to treat acne and other skin problems beta-adrenergic blockers used to control blood pressure and birth control pills. hair loss can also be caused by burns x-rays and scalp injuries. in such cases normal hair growth usually returns once the cause is eliminated. ringworm caused by a fungal infection can also cause hair loss. the causes of alopecia areata a disease that often strikes children or teenagers remain unexplained. it is thought to be an autoimmune disease meaning that the immune system revs up for unknown reasons and affects the hair follicles. in most cases the hair grows back although it may be very fine and possibly a different color before normal coloration and thickness return. although shampooing too often perms bleaching and dyeing hair do not cause baldness they can contribute to overall thinning by making hair weak and brittle. tight braiding and using rollers or hot curlers can damage and break hair and running hair picks through tight curls can scar hair follicles. in most instances hair grows back normally if the source of the problem is removed but severe damage to the hair or scalp sometimes causes permanent bald patches.
what causes hair loss?