Hair Loss: Causes and Risk Factors

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.

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.

Other 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 other possible causes of hair loss, especially if in an unusual pattern exists, include:

• Delayed shedding from stress. 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, 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.
• 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. 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. 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. 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). 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.
• 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, gemfibrozil
  • parkinson medications: levodopa
  • ulcer drugs: cimetidine, ranitidine
  • anticoagulants: coumarin, heparin
  • medications for gout: allopurinol
  • antiarthritics: penicillamine, auranofin, indomethacin, naproxen, sulindac, methotrexate
  • drugs derived from vitamin-A: isotretinoin, etretinate
  • anticonvulsants: trimethadione
  • antidepressants: tricyclics, amphetamines
  • beta blockers: atenolol, metoprolol, nadolol, propranolol
  • antithyroid agents: carbimazole, Iodine, thiocyanate, thiouracil
• 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.
• Thyroid disease. Both an overactive thyroid and an under-active 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. 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.
• Hair pulling (traction alopecia). Traction alopecia is the loss of hair from constant pulling, often the result of tightly braided hair styles.
• 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 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.