Dr. Greene’s Answer:
Pityriasis alba is Latin for white, scaly patches and it is the most common cause for them in childhood. Children with this extremely common condition develop uneven, round or oval patches after sun exposure. The patches are dry with very fine scales. Varying from 1 to 2 inches in diameter, they are most common on the face (cheeks), neck, upper trunk, and upper arms of children 3 to 16 years old.
These are completely benign, similar to a mild form of eczema. They are most common in children with dry skin. The involved patches don’t darken with sun exposure the way the surrounding skin does. Treatment involves daily lubrication with a good moisturizer (such as Aquaphor), especially whenever the skin gets wet. Sometimes topical steroid creams help. Even with no treatment at all, the spots will disappear on their own — although it may take months to years. Some people get pityriasis alba every summer during childhood. Even then, the pigmentation will eventually end up normal.
Even when the condition is effectively treated, the white patches will remain for a while. At least several weeks must pass for the newly healthy skin to adjust its color to the amount of ongoing sunlight exposure, so that it will match the surrounding skin.