Swimmers' itch: What causes it?

Swimmers' itch — also called cercarial dermatitis — is an itchy rash caused by certain parasites that normally live on waterfowl and freshwater snails. On warm, sunny days, especially in the calm water of freshwater lakes, these parasites can be released from infected snails into the water. The organisms may enter the superficial layers of your skin. They soon die and cause a skin reaction.

Swimmers' itch usually affects only exposed skin — skin not covered by swimsuits, wet suits or waders. On first exposure to these organisms, the skin reaction is usually mild — redness followed by itchy, red, raised areas. Usually the rash goes away within a few days. On subsequent exposures, the reaction can be more severe and persistent, sometimes causing blistering of the affected skin.

The Centers for Disease Control and Prevention offers these guidelines to reduce the risk of swimmers' itch:

• Avoid swimming in areas where swimmers' itch is a known problem.
• Avoid swimming near or wading in marshy areas where snails are commonly found.
• Rinse exposed skin with fresh water immediately after leaving the water. Then vigorously dry your skin with a towel.

Treatment of swimmers' itch may include:

• Anti-itch creams or ointments, such as those containing calamine lotion
• Oral antihistamines