Hair Loss (Alopecia) Causes

Folliculitis decalvans, also known as alopecia folliculitis or acne decalvans, is an inflammatory reaction in hair follicles on the scalp that causes redness (erythema) and pus-filled blisters (pustules). It leads to scarring and permanent hair loss.

Traction alopecia occurs as a result of improper hair care and prolonged use of certain hair-styling techniques. Cosmetic treatments (e.g., dyes, tints, bleaches, permanents) are generally safe; however, if treatments are done incorrectly, or if the chemicals are used for too long, the hair becomes brittle and breaks easily.

Hairstyles that pull the hair tightly, and excessive shampooing or brushing can also cause hair loss. Braiding, permanents, excessive heat, and hair straightening cause hair shaft weakness. Hair styling techniques such as hair weaving, corn rowing, and the use of hot combs to straighten hair can cause permanent hair thinning and scarring.

Stress alopecia, a type of telogen effluvium, is temporary, reversible, diffuse hair loss on the scalp that results from severe emotional or physiological stress. Normally, about 90 percent of scalp hair follicles are in the growing anagen phase, and about 10 to 15 percent are in the resting catagen and telogen phases. Stress causes anagen hairs to convert prematurely into telogen hairs, which means that more than the normal number of hairs are in the telogen phase and ready to shed.

Exposure to various drugs can induce a temporary alopecia. Patients concerned about hair loss or thinning should notify their doctor or other health care provider about medications they are taking. A number of prescription drugs, including certain medicines for arthritis, depression, heart problems, and high blood pressure can cause hair loss. Spontaneous regrowth usually occurs after the drug is stopped. The hair loss effect of some drugs can be prevented by cooling the scalp with a tight-fitting ice bag for 20 minutes or so while receiving the drug treatment.

Toxic alopecia (anagen effluvium) occurs when hair growth is disrupted during the anagen phase. The newly synthesized hair shafts weaken, and the hair breaks. Hair loss is usually quick and involves all the hairs in the anagen phase. Chemotherapy, radiotherapy to the scalp, and overdoses of vitamin A can cause toxic alopecia. Chemotherapy can cause 90 percent hair loss. The hair regrows when treatment ends.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 02 Feb 2001

Last Modified: 17 Sep 2015