Normal hair loss, hereditary baldness, male pattern baldness, androgenic alopecia

See our other health topics on Temporary hair loss and Treatments for hair loss

Your scalp and hair

Hair is a conspicuous feature in many cultural definitions of fashion, youth and sexuality. So, it is not surprising that a lot of people cringe at the first sign of thinning hair.

Most people lose between 50 and 100 strands of hair daily, with little impact. As hairs fall out naturally, new hairs grow back. So there is no need to despair if you spot a hair or two in your sink. However, with age this natural regrowth process may slow or stop, and thinning and baldness may occur. If you are concerned about it, see your doctor for an evaluation to find out if your hair loss is normal or if it is due to an underlying medical problem (see below, Other forms of baldness).

Like your skin and nails, your hair goes through a finely tuned cycle of growth and rest. Excessive hair loss can occur at any time this delicate cycle is upset.

About 90% of a person's scalp hair is continually growing, a phase that lasts between two and five years. Ten percent of the scalp hair is in a resting phase that lasts between two and three months. At the end of its resting stage, the hair goes through a shedding phase, which normally results in the growth of a new hair.

When a hair is shed, it is replaced by a new hair from the same hair follicle located just beneath the skin surface. Scalp hair grows about 1-2cm per month.

Hair is made up of a form of protein, the same one found in fingernails and toenails. Everyone, regardless of age, should eat an adequate amount of protein to maintain normal hair production. Protein is found in meat, chicken, fish, eggs, some cheese, dried beans, tofu, grains and nuts.

How does hair grow?

The human scalp contains about 100,000 hair follicles. These follicles each anchor a hair to the skin and contain the cells that produce new hairs. Normal hair grows in three phases.

	1. The anagen or follicle growing phase starts growing the new hair. This phase is genetically determined and can vary from two to five years (the average is just under three years). This phase results in a fully grown hair
	2. The catagen phase is a transition or resting stage. The hair stops growing and the hair root shrinks. The base of the follicle breaks down and the hair starts to move upwards in the follicle.
	3. The telogen or shedding/regrowth phase is a mature hair with a root, which is held very loosely in the follicle. The telogen phase generally lasts about three months. About 100 telogen hairs are lost from the human scalp each day. They either fall out or are pushed out by the next hair growing up the follicle from below.

In hereditary hair loss, the follicle becomes smaller, the anagen phase is shorter and the telogen hairs are shed faster. The hairs themselves become thinner and shorter because of the shorter growth phase. Levels of the male hormone testosterone and another hormone derived from it (dihydrotestosterone; DHT), are involved in the regulation of hair growth.

Hereditary baldness

The most common type of hair loss starts in males from about the age of 30, but could occur at any age past puberty. It is known as androgenic alopecia or male pattern baldness. It is thought to be hereditary and is also dependent on the extent to which the male hormone testosterone is converted in the scalp to another hormone dihydroxytestosterone. Androgenic alopecia accounts for 99% of hair loss in men.

How quickly or slowly baldness develops, and the pattern of hair loss, appear to be genetically determined. Although this type of baldness can also affect women, the pattern of baldness is different in males and females.

Male baldness usually begins with progressive thinning at the hairline, followed by the appearance of a thinned or bald spot on the crown of the head. Women with hereditary baldness rarely develop bald patches. Instead, they experience a general thinning of their hair.

Norwood-Hamilton Scale of progressive hair loss

Unlike hair loss resulting from disease or other nonhereditary factors, hair loss due to hereditary baldness is permanent.

Other forms of baldness

Hair loss that is not hereditary may be caused by pregnancy, hormonal or other medicines, severe nutritional deficiencies, chemotherapy, autoimmune disorders, an underactive or overactive thyroid gland or scalp trauma, including reactions to hair care products and hair grooming methods. (See the topic on temporary hair loss for more detail.)

When should you seek medical advice?

You should seek medical advice for hair loss if:

• you are a woman who has recently given birth
• you have been diagnosed with an autoimmune disorder such as systemic lupus erythematosis, nutritional deficiency or thyroid disease
• you have been recently treated with chemotherapy or have used a new medication (including hormonal medications), or
• the hair loss cannot be explained by hereditary factors.

Questions you might want to ask your doctor

• What is causing the hair loss?
• Is this due to a temporary cause that will correct itself?
• Is the baldness caused by a medical disorder?
• Is it related to any medication I currently take?
• How can the problem be corrected?
• Is it diet related?
• If so, what needs to be changed in the diet?
• If baldness runs in the family, will the male family members evidently start going bald?
• How can the hair damage be repaired?
• Should I consider taking medication?
• What are the side effects of using these drugs?
• Do you recommend hair replacement?
• Is this procedure successful?

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