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Hair Loss - Cause

Losing a lot of hair (more than 100 hairs a day) can be caused by inherited factors, disease, stress, medicines, injury, aging, or hair care.

Inherited hair loss

The most common cause of hair loss is genetics—you inherit the tendency to lose hair from either or both of your parents. This is called male-pattern hair loss or female-pattern hair loss. The medical term for this type of hair loss is androgenetic alopecia.

In this type of hair loss, your genes affect how your hair grows. They trigger a sensitivity to a class of hormones called androgens, including testosterone, which causes hair follicles camera.gif to shrink. Hair follicles are the openings that hair grows from.

Shrinking follicles produce thinner hair and eventually none at all. Men generally develop bald spots on the forehead area or on the top of the head, while women often have thinning of the hair on the top of the head. About half of all people have inherited hair loss camera.gif by about 50 years of age.

Other causes of hair loss

Different types of hair loss may have different causes. Common causes of hair loss include:

  • Ringworm of the scalp, which is common in children.
  • Mental stress or physical stress, such as recent surgery, illness, or high fever. You may have a lot of hair loss 1 to 3 months after severe physical or emotional stress. Your hair usually will grow back within a few months.
  • Hair styling and products. Pulling your hair back too tightly or wearing tight braids or ponytails can cause hair loss. You may lose hair around the edge of the hairline, especially around the face and forehead. Using curling irons or dyes a lot can also result in hair loss. Hair usually grows back when you stop doing these things.
  • Age. As you age, your hair tends to break more easily, and hair follicles do not grow as much hair.
  • Poor nutrition, especially lack of protein or iron in the diet. Hair returns after you change your diet to get enough of these nutrients.
  • Thyroid diseases, including hypothyroidism and hyperthyroidism.

Other causes of hair loss include:

  • Alopecia areata, an autoimmune disease in which your immune system attacks hair follicles, resulting in round hairless patches on any area of the scalp or body. Severe cases involve many bald patches of hair or complete loss of hair on the scalp or body, although in some cases there is hair thinning without distinct patches of baldness. The hair loss usually is not permanent. Hair grows back within 1 year for many people.
  • Diseases, such as lupus, syphilis, or cancer. Hair may grow back on its own, although you may also need treatment.
  • Side effects of medicines or medical treatments, such as blood thinners (anticoagulants) or chemotherapy. Hair usually grows back after you stop using the medicines or when the treatment is over.
  • Trichotillomania, a compulsive behavior in which a person pulls hair out of the scalp, eyelashes, or eyebrows. There is usually mounting tension before pulling and a feeling of relief afterward. Trichotillomania often results in noticeable hair loss.
  • Injury to the scalp, including scarring.
  • Changes in hormone levels. Childbirth, taking birth control pills, or changes in a woman's menstrual cycle can affect the hair growth cycle and cause hair loss. Hair usually will grow back.

    This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http:// cancer .gov or call 1-800-4-CANCER.

    WebMD Medical Reference from Healthwise

    Last Updated: March 12, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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