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Hair Loss Causes and Risk Factors
Hair loss (alopecia) is a tendency of hair follicles to stop producing hair growth, leading to a decrease in the amount of hair. Although alopecia can occur anywhere on the body, it is especially distressing when it affects the scalp. It usually develops gradually and may be patchy or diffuse. Androgenic alopecia - the most common hair loss cause The most common cause of hair loss is Androgenic alopecia - the genetic predisposition for hair loss inherited from either or both of parents. Almost all people have some degree of androgenic alopecia. Visible changes occur in most people by the age of 50 years4. The main cause of androgenic alopecia in men and women involves a genetic sensitivity to a dihydrotestosterone (DHT), a derivative of the male hormone testosterone. DHT causes hair follicles to shrink and induces miniaturization of hair. Shrinking follicles produce thinner hair, and eventually fail to produce new hairs at all. Androgsenic alopecia accounts for more than 95% of hair loss cases in men. By the age of 35 two-thirds of American men will experience some degree of perceptible hair loss and by the age of 50 about 85% of men have significantly thinning hair. Androgenetic alopecia in men (male pattern baldness) is generally characterized with the onset of a receding hairline and thinning crown. Hair on the forehead area or on the top of the head appear to be the most sensitive to DHT. Hair on the sides and back of the head do not possess this genetic trait and therefore are not affected. In women androgenetic alopecia (female pattern baldness) can begin at puberty, but is most often occurs after menopause. Women have an overall thinning of the hair throughout the scalp while the frontal hairline generally remains intact. Excess hair loss can have various causes. In addition to the common male and female patterns other possible causes of include: Telogen effluvium (delayed shedding from stress) Telogen effluvium is a diffuse hair shedding, often with an acute onset, caused by a major body stress. It is the most common cause after androgenic alopecia. Understanding the telogen effluvium requires knowledge about hair growth cycle. All hair has a growth phase (anagen), and a resting phase (telogen). On the scalp, growth phase lasts for 2 to 6 years (on average 3 years), while resting phase lasts about 3 months. During telogen, the resting hair remains in the follicle until it is pushed out by new growing anagen hair. In most people, 80-90% of the hair on the scalp is in the growth phase, and 5-15% in telogen phase at any given time. Telogen effluvium is triggered when a stressful event induces a large number of hairs to enter the resting stage (telogen phase) at one time. A few months later, after the stressful event, all 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 to grow within a few months. Stressful events include:
Drug-induced alopecia (side effect of medications) Drug-induced alopecia is a diffuse hair loss caused by toxic effect of the medication. This condition is usually reversible after discontinuation of the offending drug. Many commonly prescribed medications can trigger the onset of androgenic alopecia, cause temporary or even permanent hair loss. Drugs that can cause hair loss include:
Pregnancy and childbirth After pregnancy many women experience excess hair loss. During pregnancy, increased levels of estrogen prolong the growing phase of the hair cycle. However, after giving birth, estrogen levels come down and many hair enter the resting phase. Some women experience increased shedding several months after delivering a baby. This condition usually resolves completely as the hair growth cycle returns to normal. Birth control pills Birth control pills can cause drug induced shedding and trigger genetic hair loss (androgenic alopecia). Excess hair loss can occur with starting, switching, or discontinuing the pills. Women experiencing hair shedding or thinning, while taking birth control pills, usually have a genetic predisposition for hair loss. The hormonal changes that occur trigger the onset of the androgenic alopecia. The pills that are higher in progesterone compared to estrogen are more likely contribute to this process. After stopping the oral contraceptives, woman may notice hair shedding two or three months later. This may continue for six months when it usually stops. In some cases the process cannot be reversed and the woman may not regrow all lost hair. If a woman has a history of female pattern loss in her family she should consult with her doctor before going on the pill. Alopecia areata Alopecia areata is patchy hair loss. It is considered an autoimmune disease, but the cause is unknown. Sudden loss of hair from small patches on the head is a common symptom. The patch of alopecia areata is round or oval, and is completely bald and smooth. 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 long-term hair loss, or develop new patches as old patches resume hair growth. About 2% of people experience an episode of alopecia areata at some point in their lives. This form of hair loss affects both sexes equally and occurs at all ages, but is more common in children and adolescents. Iron deficiency Iron deficiency is one of the possible causes of excessive hair loss, especially in women3. Adequate levels of iron are essential to hair growth and maintenance. Some people don't have enough iron in their diets or may not fully absorb iron. Iron depletion is common to women during menstruation and pregnancy and can be corrected through proper diet or iron supplements. Protein deficiency Severe protein malnutrition may also cause hair loss2. The body will save protein by shifting growing hairs into the resting phase. Some people who go on crash diets that are low in protein, or have severely abnormal eating habits, may develop protein malnutrition. This condition can be reversed and prevented by eating the proper amount of protein and, when dieting, maintaining adequate protein intake. Thyroid disease Both hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) can cause hair loss. Hair follicles are particularly sensitive to thyroid hormones and about 30% of persons with thyroid disorder suffer from hair loss. Tinea capitis Tinea capitis (also known as Scalp ringworm) is caused by fungi called dermatophytes. They can invade the hair and skin of the scalp, leading to hair loss. Tinea capitis is especially common in children, and rarely occurs after puberty. Once infection is treated, hair generally regrows. Traction alopecia (hair pulling) Traction alopecia is the loss of hair from constant pulling, often the result of tightly braided hair styles. Braiding, corn-rows, tight pony-tails, and hair extensions are the most common styling causes. References & Resources
Last updated: August, 2010 |
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