Stress, regardless of its cause, changes the way your body works. When faced with an anxiety-provoking situation, your endocrine glands pump out adrenaline, cortisol, and other hormones. These substances have various effects on your body, including reducing blood flow to your hair follicles. The theory goes that a week or more of continual stress reduces nutrient flow to the hair for enough time to cause temporary hair loss. Get rid of the stress (or learn how to face it calmly) and give yourself a month: Your hair will return.

Medications have different effects on different people. For instance, birth-control pills may give you migraines but they may make your sister's skin break out. Aspirin may upset your mother's stomach but could be the only pain reliever that works for you. And so it is with this: a drug that makes a friend feel slightly tired might leave you with temporary hair loss. While your body can react this way with any drug, some are notorious for causing hair loss, including chemotherapy drugs, antibiotics, and antidepressants. Also, if you have had, or are scheduled for, surgery of any kind, be aware that anesthesia can cause a week or two of temporary hair loss in some people.

Other reasons for hair loss

When worn daily for a month or more, tight hairstyles - such as cornrows, a severe ponytail, or braids - can damage the hair follicle, making it impossible for new hair to grow. This condition, called traction alopecia, is permanent. Damage to the scalp caused by chemicals used in hair color formulas, permanent waves or relaxer services, burns, or even a blow to the head, can damage hair follicles, causing permanent hair loss.

Sometimes hair loss just happens for no apparent reason. For example, a disease called alopecia areata strikes both men and women and causes diffuse thinning or even patchy baldness. In severe cases, it even causes sufferers to lose their eyelashes, eyebrows, and body hair. What is known about this disease is that it is an immune-system disorder that causes hair follicles to stop producing hair. In some people, alopecia areata is temporary, lasting from several months to several years. In other people, the condition remains, improving or worsening seemingly at whim.

In the United States, about 1 percent of the population have experienced alopecia areata, however about 90 percent of these people have had periodic episodes.