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Swimmer's Itch

Young child jumping into lake from a pier with arms up

Swimmer's itch is a skin rash caused by tiny parasites found in water. The parasite normally infects birds or mammals that live near water, but can sometimes find a human and cause an allergic reaction.

Outbreaks occur when the weather and water gets warmer. They are most common in May to early July in southern Wisconsin lakes and late June to early July in northern Wisconsin lakes.

Swimmer’s itch is not dangerous and cannot be spread from person to person, but it can be very uncomfortable.


Swimmer's Itch 101

People get swimmer’s itch when the parasites burrow into their skin. The parasites are unable to live in a human and soon die. This can happen when someone air dries after being in water where the parasite is living. Air drying gives the parasite time to burrow into the skin. The dead remains of the parasite under the skin are what cause people to have the allergic reaction we call swimmer’s itch.

Anyone can get swimmer's itch. Children are more likely to have swimmer’s itch than adults because they are more likely to air dry or spend more time close to shore where the parasite tends to be. You cannot get swimmer's itch by swallowing water.

Waterfowl, such as ducks or geese, are a common source of the parasite and should be kept away from swimming beaches. Infected waterfowl poop contains eggs of the parasite. When the poop enter the water, the eggs hatch into the first life stage of the parasite. This first stage swims around until it finds and burrows into a snail. Over the next three to four weeks, it grows into the second stage of the parasite, which is colorless and very small, so you can’t see them. When the water temperature rises, the parasites are released from the snails to go in search of their new bird or mammal host to infect. If the parasite finds a human instead, it can cause swimmer’s itch.

Symptoms can begin within minutes of getting out of the water or they can take a few days to develop. Symptoms of swimmer’s itch may include:

  • Tingling, burning, or itching of the skin.
  • Small, itchy, red pimples on the skin that look like bug bites.
  • Small blisters.

The small reddish pimples typically appear within 12 hours and reach their largest size after about 24 hours. These welts may turn into small blisters. The itching may continue for several days, but usually goes away within a week. Do not scratch because it can cause an infection. Swimmer’s itch can appear on any part of the body that was in the water.

The first time a person swims in contaminated water, they may not get swimmer's itch. Having repeated exposure to contaminated water can increase your chances of developing a rash. If you’ve had swimmer’s itch before, you may be more likely to have this allergic reaction again with more intense and immediate symptoms.

Most cases of swimmer's itch do not require going to the doctor or treatment. If you have swimmer’s itch, you may get relief by applying skin lotions or anti-itch creams to the affected area or taking an over-the-counter antihistamine. For severe cases affecting your ability to sleep or causing secondary infections, contact a doctor.

Spending more time in the water increases your chances of getting swimmer’s itch. To reduce your chances of getting swimmer’s itch:

  • Dry off with a towel immediately after leaving the water instead of air drying. This helps prevent parasites from burrowing into the skin.
  • Change out of wet swimsuits and shower as soon as possible after swimming.
  • Using water-repellant substances, such as waterproof sunscreen may make it harder for the parasite to get into the skin. However, this is not completely effective.
  • Look for signs that swimmer’s itch activity is high. If present, find another place to swim.
  • Do not feed wildlife and waterfowl, like ducks or geese, near swimming areas. Feeding encourages them to stay in the area and increases the risk of the water becoming infected with the parasite.

Questions about swimmer's itch? Contact us! Phone: 608-267-9003 | Fax: 608-261-497

Wisconsin Local Health DepartmentsRegional officesTribal agencies


Last revised January 23, 2024