Any kind of physical trauma—surgery, a car accident, or a severe illness, even the flu—can cause temporary hair loss. This can trigger a type of hair loss called telogen effluvium. Hair has a programmed life cycle: a growth phase, rest phase and shedding phase. “When you have a really stressful event, it can shock the hair cycle, (pushing) more hair into the shedding phase,” explains Marc Glashofer, MD, a dermatologist in New York City. Hair loss often becomes noticeable three-to-six months after the trauma.
Hair lost to male-pattern and female-pattern baldness won't grow back on its own, but there are medications that can help slow hair loss and even regrow hair. Minoxidil (Rogaine) is a topical medicine that is available over the counter to treat men and women. Finasteride (Propecia) is a pill that is available to men only by prescription. Injectable cortisone may also help regrow hair lost to certain conditions.
1. Minoxidil. It’s the only FDA-approved topical nonprescription medication that can claim to regrow hair — and it should be part of any hair-loss plan if you have serious thinning, says Rogers. Minoxidil has loads of research to back it, but it requires commitment. If you quit using it, your hair will start to lose ground again. Use a 5 percent strength, like Women’s Rogaine 5% Minoxidil Foam ($30), once daily to see results in three to four months, says Rogers.

Alopecia areata - bald patches develop on the scalp, beard, and possibly eyebrows. eyelashes may fall out as well. This is thought to be an autoimmune disease, where the immune system attacks the hair follicles and leads to hair loss on the scalp and other parts of the body. However, the hair follicles are alive so there is potential for hair to regrow when the underlying problem has resolved. Growth may occur even without treatment and even after many years. In most cases hair loss only happens in a few places, leaving a few bare patches. In some cases though, the disease can advance to total loss of hair from the head (alopecia areata totalis) or complete loss of hair on the head, face and body (alopecia areata universalis). 

Pregnancy may cause many changes in the scalp hair. As the hormones fluctuate during pregnancy, a large number of women feel their hair thickens and becomes fuller. This may be related to change in the number of hairs cycling in the growth phase of hair growth, but the exact reason is unknown. Quite often, there may be a loss of hair (telogen effluvium) after delivery or a few months later which will eventually normalize.
There are many different types and forms of hair concealers. The two most popular types are hair sprays, and sprinkles and powder solids. Sprays are easy to apply compared to creams and powders. They contain chemicals and dye that can match the shade of your hair, making it fuller. However, it has a tendency to look less natural if applied haphazardly so it requires some care during application.
Finasteride is available on private prescription in a tablet form. It prevents the hormone testosterone being converted to another hormone called dihydrotestosterone (DHT), which is known to shrink hair follicles. Blocking this action can help the hair follicles to return to their normal size. It usually takes three to six months of daily use to see an effect, and the process starts again if treatment is stopped.
Scientists have put a lot of effort into investigating the cause of gray hair, and they believe they've gotten to the root of the problem. Hair gets its color from a pigment called melanin, which is produced by melanocyte cells in the hair follicles. Researchers have discovered that melanocytes endure cumulative damage over the years, which eventually leaves them unable to produce melanin. Studies have cited DNA damage and a buildup of hydrogen peroxide in the follicles as possible causes of this disruption in melanin production. Without melanin, the new hair that grows in has no pigment, which makes it appear gray, white, or silver.
If your doctor recommends it, a product like minoxidil can increase hair growth in male- and female-pattern baldness. Alopecia areata can be helped by treatment with corticosteroid creams or injections on the scalp. If your doctor thinks that nutritional deficiencies are causing your hair loss, he or she might refer you to a dietitian or other nutrition expert.

Tinea is the medical word for fungal infection, and capitis means head. Tinea capitis is fungal infection of the scalp that for the most part affects school-age children. Tinea capitis is more common in black African or African-American scalps. This condition is rare in healthy adults. Bald spots usually show broken-off hairs accompanied by a dermatitis. Oral antifungals can penetrate the hair roots and cure the infection, after which hair grows back. Sharing hats or combs and brushes may transmit tinea capitis.
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