Alopecia areata is hair loss of unknown origin. It results in small, usually round, suddenly appearing patches of complete baldness. There is no known cause. Only one in five cases has a genetic component. Sometimes alopecia areata is a result of an autoimmune disorder.

Alopecia areata is a form of hair loss that appears on the scalp, but may also occur on the beard. Sometimes it can even affect the eyebrows or eyelashes. Sometimes it is a result of stress. Alopecia areata can spontaneously correct itself, or it may respond to topical treatments such as prednisone. Injections and ultraviolet light are other treatments for this form of hair loss.

Another form of hair loss is called traction alopecia. People who wear tight braids, cornrows or ponytails can cause hair loss at places where the scalp has been pulled too tight. Nervous habits such as hair twisting can also cause traction alopecia. If the practice is stopped before the scalp develops scarring, it usually reverses the hair loss fairly quickly. Other kinds of scalp scarring, from overly hot hair treatments or the chemicals used in permanents or hair straightening, for example, may inflame follicles and cause permanent or temporary hair loss.

Some hair loss is caused by medicines such as blood thinners, chemotherapy agents, excessive use of vitamin A, birth control pills and antidepressants. This losing of hair usually reverses itself after the medication is stopped.

Many women worry about a perceived excessive losing of hair after childbirth. This is actually an issue of perception. During pregnancy, the body retains hair that would have normally fallen out every day. As pregnancy hormone levels drop, the retained hair is quickly lost. Losing several months' worth of hair is more noticeable than daily shedding, but it is only your hair returning to its normal state and is not indicative of balding.