Hair loss is related to the tendency of hair follicles to stop producing hair growth. Partial or complete loss of hair is called alopecia. Hair loss usually develops gradually and may be patchy or diffuse.

Hair is the fastest growing tissue in the body, second only to bone marrow.
The average scalp contains about 100,000 hairs.
Roughly 100 hairs are lost from your head every day.
Each individual hair survives for an average of 4 - 7 years, during which time it grows about half an inch a month.
You need to lose about 50% of your hair before hair loss becomes noticeable.
In the United States, 30 million women experience hereditary hair loss. 70% of women with thinning hair can attribute it to hereditary hair loss.
Hereditary hair loss or androgenetic alopecia is the most common form of hair loss for men, representing more than 95% of all male cases.
Androgenetic alopecia affects many more men than women. About two-thirds of men experience some degree of appreciable hair loss by the time they are 35 years old, and about 85% have significantly thinning hair by age 50.
In the United States, there has not been an elected bald President since the television age began.

The Most Common Cause Of Hair Loss

The most common cause of hair loss is genetics - inherit the tendency to lose hair from either or both of parents. The medical term for the genetic predisposition for hair loss is "androgenetic alopecia".

In androgenetic alopecia, the genes affect how the hair grows. They trigger a sensitivity to a class of hormones called androgens, including testosterone, which causes hair follicles (which hair grows from) to shrink. Shrinking follicles produce thinner hair and eventually none at all. Thus, androgenetic alopecia is caused by the body's failure to produce new hairs and not by excessive hair loss. Heredity also affects the age at which you begin to lose hair and the developmental speed, pattern and extent of your baldness.

Androgenetic alopecia accounts for more than 95% of hair loss in men. By the age of 35 two-thirds of American men will experience some degree of appreciable hair loss and by the age of 50 approximately 85% of men have significantly thinning hair.

Men generally develop bald spots on the forehead area or on the top of the head. In men, the hairs on the top of the head have a genetic sensitivity to the male hormone testosterone while the hairs on the sides and back of the head do not possess this genetic trait and therefore are not affected. For this reason hairs removed from the sides and the back (donor hair) will maintain their genetic predisposition when transplanted and continue to grow when moved to the top of the head where hair loss has occurred.

For woman, female pattern baldness is the most common type of hair loss. It can begin at puberty, but is most often seen after menopause. Women have an overall thinning of the hair throughout the scalp while the frontal hairline generally remains intact.

Other Hair Loss Causes And Risk Factors

Hair loss is not usually caused by a disease, but is related to aging, heredity, and testosterone. In addition to the common male and female patterns from a combination of these factors, other possible causes of hair loss, especially if in an unusual pattern exists, include:

Side effects of medications or medical treatments. Certain drugs used to treat gout, arthritis, depression, heart problems and high blood pressure may cause hair loss in some people. Drugs that can cause hair loss include:
- cholesterol lowering drugs: clofibrate (Atromis-S), gemfibrozil (Lopid)
- parkinson medications: levodopa (Dopar, Larodopa)
- ulcer drugs: cimetidine (Tagamet), ranitidine (Zantac)
- anticoagulants: coumarin, heparin
- medications for gout: allopurinol (Zyloprim)
- antiarthritics: penicillamine, auranofin (Ridaura), indomethacin (Indocin), naproxen (Naprosyn), sulindac (Clinoril), methotrexate (Folex)
- drugs derived from vitamin-A: isotretinoin (Accutane), etretinate (Tegison)
- anticonvulsants: trimethadione (Tridione)
- antidepressants: tricyclics, amphetamines
- beta blockers: atenolol (Tenormin), metoprolol (Lopressor), nadolol (Corgard), propranolol (Inderal)
- antithyroid agents: carbimazole, Iodine, thiocyanate, thiouracil
Delayed shedding from stress (telogen effluvium). This common form of hair loss happens two to three months after a major body stress. The stressful event induces a higher proportion of hair follicles to enter the resting stage all at the same time. A few months later, after the stressful event, all of the now-resting follicles begin to shed their hairs at about the same time. Because the stressful event happened months ago, most people do not connect it with their hair loss. It is a temporary condition, and new hairs begin growing within a few months. Stress can also trigger genetic hair loss. If your already losing hair stress will cause you to lose hair even faster.
Stressful events include:
- Physical stress - surgery, very high fever, major illness, rapid weight change.
- Emotional stress - mental illness, divorce, death of a loved one, job loss.
Inadequate protein in diet. Some people who go on crash diets that are low in protein, or have severely abnormal eating habits, may develop protein malnutrition. The body will 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 fairly easily. This condition can be reversed and prevented by eating the proper amount of protein and, when dieting, maintaining adequate protein intake.
Iron deficiency. Iron deficiency occasionally produces hair loss. Some people don't have enough iron in their diets or may not fully absorb iron. Iron deficiency is common to women during menstruation and pregnancy and can be corrected through proper diet or iron supplements.
Pregnancy and childbirth. Hair loss that is connected to pregnancy usually occurs after delivery. When a woman is pregnant, her hairs grow at very high speed. However, after a woman delivers her baby, many hairs enter the resting phase of the hair cycle. Some women experience an increase in hair loss several months after delivering a baby. This is a natural process and resolves completely in most cases.
Birth control pills. Women who lose hair while taking birth control pills usually have an inherited tendency for hair thinning (androgenic alopecia). The hormonal changes that occur trigger the onset of the androgenic alopecia. If hair thinning occurs, a woman can consult her gynecologist about switching to another birth control pill. If a woman has a history of female pattern loss in her family she should advise her doctor before going on the pill.
After the discontinuation of the oral contraceptives, woman may notice that her hair begins shedding two or three months later. This may continue for six months when it usually stops. This is similar to hair loss after the birth of a child. In some cases the process cannot be reversed and the woman may not regrow some of the hair that was lost.
Scalp infection. Infections such as ringworm can invade the hair and skin of your scalp, leading to hair loss. Once infections are treated, hair generally regrows. Ringworm, a fungal infection, can usually be treated with a topical or oral antifungal medication.
Thyroid disease. Both an overactive thyroid and an underactive thyroid can cause hair loss. Hair loss associated with thyroid disease can be reversed with proper treatment.
Patchy hair loss (Alopecia areata). Alopecia areata is classified as an autoimmune disease, but the cause is unknown. This disorder causes hair follicles to stop producing hairs. Approximately 2% of all people experience an episode of alopecia areata at some point in their lives. Sudden loss of hair from small patches on the head are a common symptom. In the vast majority of cases the condition is temporary and goes away all by itself withing 6-7 months, and hair growth in the bald patch resumes. About 10% of those who have an episode of alopecia areata experience longer-term hair loss, or new patches of hair loss as old patches resume hair growth.
Hair pulling (traction alopecia). Traction alopecia is the loss of hair from constant pulling, often the result of tightly braided hair styles.
Hair styles. Styles that pull or put tension on the hairs - such as tight ponytails or corn-rows - can cause hair loss.
Hair care. Pulling your hair back too tightly 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 continually can also result in hair loss. Hair usually grows back when these activities are stopped.
Blow-drying Blow-drying can worsen hair loss. The reason is that extreme heat damages the proteins in the hairs making them fragile and liable to break off. Brushing the hair during blow-drying causes more damage. If you use a hair dryer, it should be set on the coolest setting. Hair dyes, perms and hairsprays do not affect thinning hair.
Age. As you age, your hairs tend to break more easily, and hair follicles do not grow as much hair.