Swimmer's Itch

Swimmer's itch (also known as cercarial dermatitis) is a skin rash caused by an allergic reaction to microscopic parasites found in some waterfowl and aquatic mammals. Symptoms include itching, burning skin and small blisters. Medical attention is not usually required, and swimmer's itch can often be treated with a baking soda paste or by bathing in colloidal oatmeal.

 

An Introduction to Swimmer's Itch

Swimmer's itch, also called cercarial dermatitis, is a skin rash that is caused by an allergic reaction to certain parasites found in some birds and mammals. These microscopic parasites are released from infected snails into fresh and salt water (such as lakes, ponds, and oceans). Rather than finding a host bird or mammal, the parasite will burrow into a person's skin, causing an allergic reaction and rash.
 

Where Does Swimmer's Itch Occur?

Swimmer's itch occurs worldwide in every continent except Antarctica. In the United States, cases are commonly reported from the Great Lakes region
 

Swimmer's Itch: How Does Water Become Infected?

The adult parasite lives in the blood of infected birds, such as ducks, geese, gulls, swans, and certain aquatic mammals, such as muskrats and beavers. The lifecycle of the parasite entails the following:
 
  • The parasites produce eggs that are passed in the feces of infected birds or mammals 
  • If the eggs land in the water, the water will become contaminated
  • Eggs hatch, releasing small, free-swimming larvae
  • The larvae swim in the water in search of a certain species of aquatic snail
  • If the larvae find one of these snails, they infect the snail and undergo further development
  • Infected snails release a different type of larvae called cercariae into the water
  • This larval form then swims about, searching for a suitable host (bird, muskrat) so they can start the lifecycle over again.
 
Although humans are not suitable hosts, the larvae can burrow into the swimmer's skin, and may cause an allergic reaction and rash. However, these larvae cannot develop inside a human, and therefore, they will soon die.
 

Symptoms of Swimmer's Itch

Symptoms of swimmer's itch may include:
 
  • Tingling, burning, or itching of the skin
  • Small reddish pimples
  • Small blisters.
 
People may experience tingling, burning, or itching of the skin within minutes or days after swimming in the contaminated water. Small reddish pimples usually appear within 12 hours of contamination, and these pimples may develop into small blisters. When people scratch the affected areas, a secondary bacterial infection may occur. Itching may last up to a week or more, but will gradually go away. It is important to note that swimmer's itch is not the only rash that can occur after swimming in fresh or salt water.
 

Treating Swimmer's Itch

Most cases of swimmer's itch do not require medical attention. Helpful tips for relief from itching include:
 
  • Use a corticosteroid cream
  • Apply cool compresses to the affected areas
  • Bathe in baking soda
  • Soak in colloidal oatmeal baths
  • Apply a baking soda paste to the rash
  • Use an anti-itch lotion
  • Try not to scratch.
 
Scratching may cause the rash to become infected. If itching is severe, your healthcare provider may suggest prescription-strength lotions or creams to lessen your symptoms.
 

Is Swimmer's Itch Contagious?

Swimmer's itch is not contagious and cannot be spread from one person to another.
 

Risk Factors for Swimmer's Itch

Anyone who swims or wades in infested water may be at risk for swimmer's itch. Larvae are more likely to be present in shallow water by the shoreline. Children are most often affected because they tend to swim, wade, and play in the shallow water.
 
Once an outbreak of swimmer's itch has occurred in water, the water is not always unsafe. Many factors must be present for swimmer's itch to become a problem. However, there is no way to know how long water may be unsafe. Larvae generally survive for 24 hours once they are released from the snail. However, an infected snail will continue to produce cercariae throughout the remainder of its life.
 

Swimmer's Itch and Swimming Pools

As long as your swimming pool is well maintained and chlorinated, there is no risk of swimmer's itch.
 

Preventing Swimmer's Itch

Suggestions for reducing your risk of developing swimmer's itch include:
 
  • Do not swim in areas where swimmer's itch is a known problem or where signs have been posted warning of unsafe water
  • Do not swim or wade in marshy areas where snails are commonly found
  • Towel-dry or shower immediately after leaving the water
  • Do not attract birds (for example, by feeding them) to areas where people are swimming
  • Encourage health officials to post signs on shorelines where swimmer's itch is a current problem.
 
 
 
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Written by/reviewed by: Arthur Schoenstadt, MD
Last reviewed by: Arthur Schoenstadt, MD