My husband and I recently saw a series of white spots on the back of my daughter's leg. These became more prevalent this summer when we were out in the sun and she became tanner. At first we thought she scraped her leg on the pool deck, but a friend told me it was some kind of yeast infection of the skin and that I should rub dandruff shampoo on it. My husband and I have become concerned because we have not heard of this before.

E.M.

It sounds like your daughter has tinea versicolor. This is a skin infection caused by the yeast Malassezia furfur, also known as Pityrosporum orbiculare or Pityrosporum ovale. The patches, which also can occur on the limbs, are scaly and vary in color -- hence the name "versicolor." In light-skinned people, the lesions can appear darker than the surrounding skin, while in dark-skinned people, the reverse is seen. Since the infected skin cannot tan normally, the patches are much more noticeable after being exposed to the sun.

Tinea versicolor causes no permanent damage to the skin and has no serious complications. The only real effect of the infection is the cosmetic change. There are several ways to treat this infection. The cheapest way is to apply selenium sulfide-containing dandruff shampoo (such as Selsun Blue) for about 10 minutes for three or four nights. (At least some cases of dandruff are caused by the same yeast.) Antifungal creams such as clotrimazole (Lotrimin and others) are as effective as the dandruff shampoos -- perhaps even more so -- but can be expensive if you need to apply them to a large area. Oral agents such as itraconazole (Sporanox) and ketoconazole (Nizoral) are also very effective, but they can have side effects and also can be costly. After treatment, it can take several weeks for the skin color to return to normal. If there is hypopigmentation (a loss of skin pigment), normal skin color will not be restored until the areas are exposed to the sun and tanned.