What is temporary, or abnormal, hair loss?

Hair loss can be normal (hereditary) or abnormal (usually temporary). Abnormal (non-hereditary) hair loss can be due to many causes, including nutritional deficiencies, disease, medications, reactions to hair products, stress, (also for women, pregnancy). About half of the population experiences normal hair loss by the time they are aged 50 years. However, people who notice their hair shedding in large amounts after combing or brushing, or whose hair becomes thinner or falls out, should consult their doctor.

Causes of temporary hair loss

Possible causes and risk factors for abnormal (temporary) hair loss:

• Childbirth. When a woman is pregnant, she does not lose as much hair as usual. However, after she delivers her baby, many hairs enter the resting stage of the hair cycle. Within two to three months after delivery, some women may see large amounts of hair coming out in their brushes and combs. This condition usually corrects itself.
• High fever, severe infection, flu. From four weeks to three months after a person has a high fever or a severe infection or flu, he or she may be shocked to see a lot of hair falling out. This condition usually corrects itself but it may require treatment.
• Thyroid disease. Both an overactive and underactive thyroid gland can cause hair loss. The hair loss associated with thyroid disease can be reversed with proper treatment.
• Inadequate protein in diet. Some vegetarians, people who go on crash diets that exclude protein, and those with severely abnormal eating habits, may develop protein malnutrition. When this happens, a person's body will help to save protein by shifting growing hairs into the resting phase. Massive hair shedding can occur two to three months later. Hair can then be pulled out by the roots. This condition can be reversed by eating the right amount of protein.
• Medications. Some prescription drugs can cause temporary hair shedding in a small percentage of people. Examples of such drugs are blood thinners, some drugs used to treat gout and arthritis and some medications for heart problems.
• Cancer treatment drugs. Certain types of drugs used in chemotherapy will cause hair cells to stop dividing. Hair shafts become thin and break off as they exit the scalp. This can occur one to three weeks after chemotherapy. The patient may lose up to 90% of their natural scalp hair. The hair will grow back after treatment ends.
• Birth control pills. Women who lose their hair when taking birth control pills usually have an inherited tendency towards hair thinning.
• Low serum iron. Iron deficiency sometimes produces hair loss. Low iron can be detected by laboratory tests and corrected with iron replacement (iron tablets or injections, or simple dietary adjustment).
• Major surgery or chronic illness. Anyone who has had a major operation - a tremendous shock to the system - may notice increased hair shedding one to three months afterwards. This condition reverses itself within a few months. People who have a chronic (long term) illness may shed hair indefinitely.
• Alopecia areata. In this type of hair loss, hair usually falls out, resulting in totally smooth, round patches about the size of a coin or larger. This disease may affect children, women or men of any age.

Hair loss with other symptoms

See your doctor if you experience hair loss at the same time as having any of the following symptoms:

• skin problems
• breathing problems
• poor appetite or unexplained weight loss
• vomiting
• fever
• pain
• constipation or diarrhoea.

Normal hair loss

Androgenic alopecia is the most common type of hair loss and is often called "male pattern baldness", hereditary baldness or normal hair loss. The hair usually thins out first in the front of the scalp and the thinning moves progressively to the back and top of the head.

Related topics

Also see: Treatments for hair loss and Hair loss in women

Material adapted from myDr Australia and HealthScout. Reviewed in New Zealand by Dr Garsing Wong, February 2005.