Cercarial Dermatitis (Swimmer's Itch)

Medically Reviewed by Zilpah Sheikh, MD on April 17, 2024
5 min read

A swimmer's itch is an allergic reaction to certain parasites that typically infect specific mammals and birds. This allergic reaction is also known as cercarial dermatitis, which develops as a skin rash. 

The microscopic parasites responsible for swimmer's itch contaminate fresh water and salt water after being released from infected snails, though it's rarer to get swimmer's itch from salt water. If you swim in such parasite-infested water, the parasite will burrow into your skin, resulting in an allergic reaction. Swimmer's itch is common around the world and is more prevalent during the summer months.

Swimmer's itch happens when parasites from infected aquatic snails burrow into your skin after you swim in contaminated water. 

Swimmer's itch parasites

Adult parasites thrive in the blood of an infected bird or mammal, especially those that live in or near water such as ducks, swans, or raccoons. The adult parasites then produce eggs that are passed in the infected bird or mammal's excrement. If these eggs end up in the water, they hatch into microscopic larvae, which look for specific aquatic snails to infect.

Once they infect the snails, they live off the hosts' blood before maturing into adults. They then produce a different kind of microscopic larva called cercariae (hence the name cercarial dermatitis).

Once the infected snail releases the cercariae in the water, it swims in search of an aquatic bird or mammal. Generally, humans are not a perfect host for cercariae, but the parasite can burrow into the skin, causing allergic reactions and itchy rashes. Since the larvae cannot survive in the human body, they eventually die in the skin. 

Is swimmer's itch contagious?

You can't catch swimmer's itch from someone else. This allergic reaction can't be passed from person to person.

Most people, while describing their condition, will say they got a rash from lake water or a rash from swimming. Here are some of the most common symptoms of a swimmer's itch.

  • Burning, itching, or tingling sensation in the affected skin
  • Small, itchy blisters
  • Red, sore pimples

In a case of cercariae infection, you're likely to experience an unusual tingling, burning, or itching sensation after a few minutes or days following a swimming session. Scratching will lead to a rash, which may lead to small blisters. Persistent scratching may result in other bacterial infections. However, the itching will subside after a few days or within a week. 

Even so, you may develop more severe symptoms if you often swim in contaminated water. The more you're exposed to contaminated water, the more frequent and intense your case of swimmer's itch can be.

There are several types of skin reactions similar to cercarial dermatitis, which can make it hard to tell if your condition is a swimmer's itch. For example, insect bites, jellyfish stings, or bacterial infections may cause similar symptoms on your skin. There are no specific tests for cercarial dermatitis. To diagnose swimmer's itch, the doctor may ask you specific diagnostic questions to identify the allergy. Your doctor will want to know:

  • When you first started feeling the itchy sensation
  • If you've had a swimming session with the past 24 hours
  • If other people who were exposed to the water developed similar symptoms

Your doctor may also ask about your medical history, any allergies, and whether you're taking any special medications or supplements.

Swimmer's itch treatment home remedies

Swimmer's itch can be treated using available home remedies. Notable remedies recommended by the CDC include the following:

  • Using anti-itch corticosteroid cream
  • Applying baking soda paste
  • Applying cool compresses
  • Bathing with colloidal oatmeal or Epsom salts

How long does swimmer's itch last?

After you swim in contaminated water, you may notice small, red pimples within 12 hours. These spots may become blisters and will probably last around a week. 

If you swim in water that has the parasite, you're likely to develop a swimmer's itch. Swimming or wading through shallow water near a shoreline where snails can thrive also exposes you to cercariae dermatitis. Children are more susceptible to swimmer's itch since they tend to play near such water bodies. If you've had a swimmer's itch before, a subsequent exposure can result in severe reactions. However, a well-maintained swimming pool that is regularly chlorinated is generally safe and doesn't pose the risk of a swimmer's itch infection. 

If you swim in a pond, lake, or the ocean, there are a few steps you can take to lower your risk of getting swimmer's itch:

  • Check for any signs warning of unsafe water before you get in.
  • As soon as you get out of the water, towel off or take a shower.
  • Avoid swimming in shallow or marshy waters that could attract snails.

A swimmer's itch infection will cause you to scratch the affected area aggressively. This reaction can lead to bacterial infection. Such conditions may require treatment using antibiotics, special cream, or ointment. Call your doctor if your symptoms persist, you develop new ones, or your fever is 100.4 F (38 C) or higher.

Swimmer's itch is an allergic reaction caused by parasites that live in shallow fresh water and salt water. If you swim in a lake, pond, or the ocean, towel off or shower as soon as you get out of the water to reduce your risk of swimmer's itch. If you notice blisters or pimples, try not to itch. The allergic reaction should start to improve within a week, but talk to your doctor if your symptoms persist. 

How do you get rid of swimmer's itch?

Most of the time, swimmer's itch will get better on its own. But applying anti-itch corticosteroid cream, cool compresses, Epsom salts, colloidal oatmeal, or baking soda pastes may help you stop itching.