Swimmer’s itch is the name for a skin rash that appears due to an allergic reaction to certain parasites. Doctors refer to this condition as cercarial dermatitis. The parasites that cause swimmer’s itch are found in bodies of fresh and salt water, where they may come into contact with humans.

If a person enters water where these parasites are present, they may come into contact with them. The Centers for Disease Control and Prevention (CDC) note that if this happens, the parasite may burrow into the person’s skin.

This can cause an allergic reaction, causing a rash to form. This rash is known as swimmer’s itch.

In this article, we discuss the causes of swimmer’s itch, the symptoms, treatment, and more.

The larval parasite called cercaria is present in both land and water snails. When the parasite leaves a snail, it can enter both fresh and salt water, looking for its next host.

The parasite’s ideal host includes several birds, such as geese, ducks, swans, and gulls, and certain mammals, including muskrats and raccoons.

If a person enters infected water, they may come into contact with the parasite. The parasite may mistakenly penetrate the skin of a person. This can cause the person to have an allergic reaction. The allergic reaction causes the person to develop a patchy, inflamed, pinpoint skin rash, known as swimmer’s itch.

The American Osteopathic College of Dermatology notes that swimmer’s itch is not severe and often goes away without treatment after 1 week. In rare cases, it can affect a large portion of a person’s body and become more severe.

Swimmer’s itch is most commonly present in people who engage in recreational water activities in bodies of fresh water.

The adult form of the parasite that causes swimmer’s itch is a trematode. According to the CDC, this parasite is often present in the blood of infected birds and mammals.

The parasites produce eggs that pass out of the infected animal via its feces.

Sometimes these eggs end up in water, where they hatch, releasing the larval form of the parasite into the water. The larval parasite swims to find its next host, which is a type of aquatic snail.

If the larvae find a snail, they will infect it. When infecting a snail, the larvae multiply and develop further. The infected snail then releases another larval form of the parasite called cercaria into the water.

The cercaria swims in the water, searching for a suitable host where it can continue the next phase of its life cycle and become a trematode.

Once a snail releases the cercaria parasites into water, they survive for around 24 hours. They then die, and the infected water is safe again.

However, an infected snail will continue to produce cercaria larvae for the remainder of its life. This means the release of parasites may continue until all infected snails have died.

For the infection to spread to other snails present in the water, infected birds or mammals must again release the parasite into the water through their feces.

Common symptoms of swimmer’s itch include:

  • a small rash on the skin
  • itchy skin
  • a tingling or burning sensation on the skin
  • small pimples
  • small blisters

According to the CDC, a person may experience tingling, burning, or itching of the skin within minutes or days of swimming in contaminated water.

Small pimples may appear within 12 hours. These pimples can then develop into small blisters.

A person may have an itching sensation for a week or more, but it will often gradually go away without treatment. Swimmer’s itch tends to go away on its own after 1–3 weeks.

An allergic reaction causes swimmer’s itch. This means that the more often a person exposes themselves to contaminated water, the more likely it is they will develop more serious symptoms.

The larval form of the trematode parasite is often present in fresh and salt water. This parasite swims around in search of a new host.

A human is not a suitable host for the parasite. However, the parasite can mistakenly burrow into a human’s skin. When the parasite enters the skin it can cause an allergic reaction that causes swimmer’s itch to develop.

Because a human is not a suitable host for the parasite, the larvae will not develop inside a human. This means that over time the larvae soon die.

Can it spread to others?

Swimmer’s itch is not contagious. This means the condition cannot spread to another person.

In most cases, a person with swimmer’s itch will not require treatment.

A person may wish to treat their rash in one of the following ways:

  • using a corticosteroid cream
  • applying a cool compress to the rash
  • bathing the rash in Epsom salts or baking soda
  • soaking the rash in an oatmeal bath
  • applying a paste of water and baking soda to the rash
  • using an anti-itch lotion

A person should try to avoid scratching the rash. If they do scratch it, they may break the skin, which can cause the rash to become infected, and require medical treatment.

An infected rash may ooze yellow or green fluid. It may also swell up or crust over. Pain and warmth in the area of the rash is a sign that an infection may be present.

To prevent swimmer’s itch, a person may wish to be careful about where they choose to swim.

They should also avoid:

  • swimming in water where a known infection is present
  • swimming in water where signs are present that warn about unsafe water
  • swimming or wading in water in areas where the snails are often present, such as marshy areas

If a person does go swimming in fresh or salt water, they should always towel dry or shower immediately after leaving the water.

The CDC also recommends that people encourage health officials to post signs near water where swimmer’s itch is a current problem.

Swimmer’s itch is generally not dangerous and symptoms should go away on their own without treatment.

However, if a person has a particularly large rash that covers a big portion of their body, they may wish to contact a doctor.

Swimmer’s itch is the name for a rash that forms once a person comes into contact with the cercaria parasite. This parasite is the larval form of the trematode parasite.

Snails release the parasites into water, where they search for their next host. Once the larvae enter the host, they can continue their life cycle.

If a person swims in infected water and comes into contact with the parasite, it may mistakenly burrow into the person’s skin.

A person may then experience an allergic reaction to this parasite, which causes them to develop swimmer’s itch. Swimmer’s itch often appears as an inflamed, itchy rash that goes away over time without the need for treatment.