Swimmer itch (or swimmer's itch) is a patchy, red rash that develops when the skin comes into contact with fresh or salt water contaminated with parasites. It often appears within 48 hours of exposure to the water and may last up to a week. It is also referred to by several other names, including “sea lice,” “duckworms,” “duck fleas,” “rice paddy itch” or “clam digger's itch.”

The most common causes of swimmer itch are trematode parasites. These parasites are found first in infected snails, and later in infected birds and mammals. At various times, the snails and mammals each release these parasites into the water. People who swim in such water may come into contact with these parasites, causing a skin reaction known as swimmer itch.

Swimmer itch typically produces a mild reaction in which the skin becomes red and raised. Itchy areas, sometimes resembling small pimples or blisters, appear. The skin may also tingle or burn. In most cases, only skin not covered by swimsuits, wet suits or waders is affected.

Symptoms associated with swimmer itch normally disappear without treatment. In some cases, patients may use creams and ointments to treat symptoms associated with this condition.