My 8-year-old boy is presenting a localized hair loss since approximately 10 days. What is causing this?

An average human scalp contains about 100,000 hairs. Even when most of these hairs remain healthy, it is little consolation to the child with hair loss. Sergio, I expect that your 8-year-old's hair loss concerns him even more than it concerns you.

Hair loss in children is much more common than most people suspect. Catherine Wiley, M.D., of the Connecticut Children's Medical Center, estimates that hair loss is responsible for 3% of all pediatric office visits. The list of all the possible causes for hair loss is exceedingly long. Thankfully, the great majority of children who lose their hair do so from one of four causes -- all of which usually resolve with the appropriate treatment:

1. A fungal infection similar to athlete's foot is the most common cause of hair loss in children. Tinea capitis is the technical name for this scalp infection (tinea pedis is the name if the infection is on the foot). Tinea capitis is rare after puberty. Children with tinea capitis usually have patchy hair loss with some broken-off hairs visible just above the surface of the scalp. The patches of hair loss are usually round or oval, but sometimes irregular. Sometimes the hairs are broken right at the surface, and look like little black dots on the scalp. Sometimes gray flakes or scales are seen. Treatment usually requires an oral anti-fungal medication that can be prescribed by your doctor. The medication must be taken for approximately 2 months, but is very effective at curing the infection and restoring the hair. Sometimes use of a shampoo containing 2.5% selenium sulfide is also necessary to treat this infection and to reduce the contagiousness of children with tinea capitis.

2. Alopecia areata (which means "localized baldness") is the sudden appearance of sharply circumscribed round or oval patches of hair loss. These patches are smooth -- without inflammation, scaling, or broken hairs. They appear literally overnight, or sometimes over a few days. Sometimes the hairs around the border of the bald spots are very easily plucked, and look like exclamation points due to the swollen bulb at the base. Alopecia areata is thought to be caused by the body's immune system attacking some of the hair follicles. At any given moment about 1 per 1,000 children has alopecia areata. About 25% of these children will also have pitting or ridging of the nails. Overall, the outlook for children with alopecia areata is quite good. With appropriate treatment, about 95% will have all of their hair back within one year -- many will have it much sooner. Children with alopecia areata should be under the care of a dermatologist, a physician who specializes in the treatment of skin disorders. About 5% of children with alopecia areata will go on to develop alopecia totalis -- the loss of all the hair on the scalp. Some of these will develop alopecia universalis -- the complete loss of body hair. A wide variety of treatments are available, mostly aimed at suppressing or distracting the immune system. The National Alopecia Areata Foundation is a valuable resource for those dealing with this condition.