Hair loss usually develops gradually and may be patchy or all over (diffuse). You lose roughly 100 hairs from your head every day. The average scalp contains about 100,000 hairs.

Each individual hair survives for an average of 4 1/2 years, during which time it grows about 1/2 inch a month. Usually in its 5th year, the hair falls out and is replaced within 6 months by a new one. Genetic baldness is caused by the body's failure to produce new hairs and not by excessive hair loss.

Both men and women tend to lose hair thickness and amount as they age. Baldness is not usually caused by a disease. It is related to aging, heredity, and testosterone. Inherited or "pattern baldness" affects many more men than women. About 25% of men begin to bald by the time they are 30 years old, and about two-thirds are either bald or have a balding pattern by age 60.

• Typical male pattern baldness involves a receding hairline and thinning around the crown with eventual bald spots. Ultimately, you may have only a horseshoe ring of hair around the sides. In addition to genes, male-pattern baldness seems to need the male hormone, testosterone. Men who do not produce testosterone (because of genetic abnormalities or castration) do not develop this pattern of baldness.
• Some women also develop a particular pattern of hair loss due to genetics, age, and male hormones (which tend to increase in women after menopause). The pattern is different from that of men. Female pattern baldness involves a thinning throughout the scalp. The front hairline generally remains intact.

A sudden physical or emotional stress may cause one-half to three-quarters of the hair throughout your scalp to shed (called Telogen effluvium). You will notice hair coming out in handfuls while you shampoo, comb, or run your hands through your hair. You may not notice this for weeks to months after the episode of stress. The hair shedding will decrease over 6 - 8 months.

Cause of this type of hair loss are:

• High fever or severe infection
• Childbirth
• Major surgery, major illness, sudden blood loss
• Severe emotional stress
• Crash diets, especially those that do not contain enough protein
• A number of medications, including retinoids, birth control pills, beta-blockers, certain antidepressants, NSAIDs (including iburpofen) and calcium channel blockers

Some women ages 30 - 60 may notice a thinning of the hair that affects the entire scalp. The hair loss may be heavier at first, and then gradually slow or stop. There is no known cause for this type of hair loss.

Other possible causes of hair loss, especially if it is in an unusual pattern, include:

• Alopecia areata -- bald patches that develop on the scalp, beard, and, possibly, eyebrows. Eyelashes may fall out as well.
• Autoimmune conditions such as lupus
• Burns
• Certain infectious diseases such as syphilis
• Excessive shampooing and blow-drying
• Thyroid diseases
• Nervous habits such as continual hair pulling or scalp rubbing
• Radiation therapy
• Tinea capitis (ringworm of the scalp)
• Tumor of the ovary or adrenal glands

Hair loss from menopause or childbirth often returns to normal 6 months to 2 years later.

For hair loss due to illness (such as fever), radiation therapy, medication use, or other causes, no treatment is necessary. The hair will usually grow back when the illness has ended or the therapy is finished. You may want to wear a wig, hat, or other covering until the hair grows back.

Hair weaves, hair pieces, or changes of hair style may disguise hair loss. This is generally the least expensive and safest approach to hair loss. Hair pieces should not be sutured to the scalp because of the risk of scars and infection.

Call your doctor if:

• You are losing hair in an unusual pattern
• You are losing hair rapidly or at an early age (for example, in your teens or twenties)
• You have any pain or itching with the hair loss
• The skin on your scalp under the involved area is red, scaly, or otherwise abnormal
• You have acne, facial hair, or an abnormal menstrual cycle
• You are a woman and have male pattern baldness
• You have bald spots on your beard or eyebrows
• You have been gaining weight or have muscle weakness, intolerance to cold temperatures, or fatigue

A careful medical history and examination of the hair and scalp are usually enough to diagnose the cause of your hair loss.

Your doctor will ask detailed questions such as:

• Are you losing hair only from your scalp or from other parts of your body as well?
• Is there a pattern to the hair loss, like a receding hairline or thinning or bald areas on the crown, or is the hair loss throughout your head?
• Have you had a recent illness or high fever?
• Do you dye your hair?
• Do you blow dry your hair? How often?
• How often do you shampoo your hair?
• What kind of shampoo, hair spray, gel, or other product do you put on your hair?
• Have you been under unusual stress lately?
• Do you have nervous habits that include hair pulling or scalp rubbing?
• Do you have any other symptoms like itching, flaking, or redness of your scalp?
• What medications do you take, including over-the-counter drugs?

Tests that may be performed (but are rarely needed) include:

• Microscopic examination of a plucked hair
• Skin biopsy (if skin changes are present)

Ringworm on the scalp may require the use of an oral drug, such as griseofulvin. Creams and lotions applied to the affected area may not get into the hair follicles to kill the fungus.

See also:

• Alopecia areata
• Female pattern baldness
• Male pattern baldness

Hair diseases. In: Habif TP, ed. Clinical Dermatology. 4th ed. St. Louis, Mo: Mosby; 2004:chap 24.

Diseases of the hair. In: Rakel P, ed. Conn’s Current Therapy 2008. 57th ed. Philadelphia, Pa: WB Saunders; 2008: chap 195.