Dr. Greene, I was giving my nephew a bath the other night and noticed white patches on his upper arms. Is this normal? Are they a sign of malnutrition? They never feed him any greens or fruits -- just cereal and chicken nuggets. We are worried about these spots. He is turning 3 years old, and we fear he is not growing up healthy.

Every year as the final weeks of summer come to a close, I am asked by parents on the phone, in the office, and online about white patches that their children have developed. It's almost a Labor Day tradition.

Fun in the sun often brings out these white spots -- especially noticeable at the end of the summer. While a healthy, balanced diet of whole foods is very beneficial, diet is probably not responsible for your nephew's white patches. Many different conditions can produce new white patches in children; I will highlight two of the most common.

Doctors call one of these conditions pityriasis alba, which is Latin for white, scaly patches. 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. Using sunscreen can decrease the appearance of the patches by inhibiting the skin around them from darkening. 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.

The other extremely common white-patch condition is called tinea versicolor. This is a mild, superficial fungal infection, somewhat similar to ringworm (true ringworm can also result in white patches). Since the affected skin doesn't change color well with sun exposure, it usually becomes apparent as white patches during the summer months. In the winter it may seem to disappear, or even seem to become slightly darkened patches as the surrounding skin gets paler (this is where the name versicolor comes from).

Tinea versicolor is most common in adolescents and young adults 15 to 30 years old (although it can certainly happen at any age). The infection is chronic and recurs easily, but it causes no other health problems. People are most susceptible to the fungus during hot months in humid areas. Taking steroids, excessive sweating, wearing tight-fitting clothing, and chronic illness can all predispose a person to tinea versicolor, but someone without any of these factors can still get this mild infection.

The patches of tinea versicolor can appear white, tan, or pink. The white patches look very similar to pityriasis alba. There are two good ways to tell them apart.

The most reliable way is to have a doctor gently scrape the white patch, dissolve the scrapings in potassium hydroxide, and look at what is left under a microscope. The classic "spaghetti-and-meatball" appearance of budding yeast confirms the diagnosis of tinea versicolor.