A number of events or circumstances can interrupt the normal cycle of hair growth and cause excessive hair loss, including heredity, hormones and medication. Hair loss may be temporary or permanent depending on the cause.

About half of the hairs in an affected area need to be shed before hair loss is typically noticeable. However, when this occurs, excessive hair loss is usually visually apparent. An unusually high number of hairs discovered on a pillow or hairbrush are also common indicators that abnormal hair loss may be occurring. Androgenetic alopecia in men (male pattern hair loss) may begin as early as the teenage years (premature male pattern hair loss) and is typically defined by hair loss around the temples and crown area. This may result in partial (receding hairline) or complete baldness.

Androgenetic alopecia in women (female pattern hair loss) tends to cause less hair loss, usually consisting of thinning near the front or side areas. Women with female pattern baldness rarely go completely bald and do not usually experience any significant hair loss until around the time of menopause.

Alopecia areata (patchy baldness) usually occurs in small areas on the scalp and sometimes on other areas of the body such as the face. Hairs that are easily pulled or tugged out of the scalp without resistance often indicate the presence of alopecia areata.

Hair loss that occurs in conjunction with an unusually stressful event (e.g., pregnancy, menopause) or serious medical condition (e.g., cancer) is usually reversible and may indicate telogen effluvium (hair loss following a stressful event).

Hair loss is not usually a cause for concern. However, it can be an early sign of certain diseases (e.g., diabetes, systemic lupus erythematosus, thyroid disorders). Hair loss may also develop as the result of poor nutrition (e.g., iron deficiency), skin damage or as a side effect of certain medications.

In general, individuals should consult a dermatologist if any of the following occurs:

• Rapid hair loss
• Hair loss in patches
• Hair loss at an early age (e.g., teenage years, 20s)
• Hair loss begins soon after starting a new medication
• Facial hair loss (e.g., balding on beard or eyebrows)
• Hair loss with itching, skin irritation, redness, scaling, pain or other abnormalities