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Swimmer's itch (cercarial dermatitis) is a burning or itchy rash caused by an allergic reaction to a waterborne parasite that burrows into the top layer of skin. The rash usually produces tiny bumps or blisters.

Because swimmer's itch is an allergic reaction, repeated exposure to infected water can increase a person's sensitivity and result in worse symptoms with each subsequent exposure.

Swimmer's itch isn't serious and usually resolves without medical treatment within one week. At-home remedies — soothing lotions, colloidal oatmeal baths or baking soda baths — may lessen symptoms.