from Lawrence E. Gibson, M.D.Click here to view the full reply on Mayo Clinic.
Generally, a white patch on skin isn't cause for concern. Sometimes a small area of skin becomes irritated or develops mild eczema, which results in a patch of skin that's lighter in pigment than is the skin around it. This is particularly common in children who have allergies, asthma or eczema. Your son's doctor may recommend applying moisturizer to the affected skin and avoiding harsh or drying soaps.
Another possible cause of a white patch on skin is a superficial yeast infection (tinea versicolor), which may cause the skin to look either lighter or sometimes darker than normal. In this case, treatment may include antifungal creams or shampoos.
If the white patch on your son's arm continues to enlarge or if additional white patches appear in other places, consult a dermatologist for an evaluation. Various other skin diseases — including psoriasis and vitiligo — also may cause a light or white patch on skin.
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