What to know about swimmer's itch, a rash caused by a tiny parasite found in water contaminated by animal poop

• Swimmer's itch is a rash caused by a common parasite found in lakes and oceans.
• The parasite thrives in water-dwelling birds, mammals, and snails, but it sometimes infects humans by mistake.

Cases of swimmer's itch occur every year, usually in early summer when the water is warmest. The rash, which can appear as small red bumps on the skin, is caused by microscopic parasites that reproduce in lakes, ponds, and oceans. If the parasite larvae gets under your skin, it can cause an itchy but otherwise benign rash.

The parasite doesn't affect humans in the long term, as the larvae die shortly after entering the body. But with repeated exposures, the immune system learns to recognize and respond to the threat, according to the Centers for Disease Control and Prevention. The more you swim in contaminated waters, the more intense and immediate the rash will be.

To prevent swimmer's itch, avoid swimming in warm, marshy waters where ducks and other waterfowl could be infected with the parasite. Many local health departments manage reports of swimmer's itch by posting signs around bodies of water where people have contracted it.

If you do contract swimmer's itch, most cases can be resolved with home remedies, like over-the-counter corticosteroid cream or Epsom salt baths.

Swimmer's itch is uncomfortable but mostly harmless

Symptoms of swimmer's itch may include tingling, burning, or itchy skin with small red bumps or blisters, according to the CDC.

The welts might look like bug bites, except they show up en masse minutes or days after a swim in untreated water. Exposed skin not covered by a swimsuit (ie. arms and legs) is most commonly affected.

If left alone to heal, the rash will clear up within a week, according to Mayo Clinic. The clinic recommends seeking medical care if the bumps linger for more than a few days or develop pus.

Scratching at the rash, however itchy it may be, increases the risk that the area will become infected with a more dangerous bacteria.

The CDC recommends using anti-itch creams or home remedies to relieve the itch, including the following tips:

• Use corticosteroid cream (available over-the-counter).
• Apply cool compresses to the affected areas.
• Bathe in Epsom salts or baking soda.
• Soak in colloidal oatmeal baths.
• Apply baking soda paste to the rash.

Preventing swimmer's itch

While the possibility of swimmer's itch shouldn't keep you from exploring natural bodies of water this summer, there are a few steps you can take to reduce your risk.

Avoid swimming spots that are known to be contaminated with any type of parasite, as some water-dwelling organisms can cause infections far more dangerous than swimmer's itch.

The parasite that causes swimmer's itch is more likely to be present in warm, shallow water, so children are more likely to be infected compared with adults.

Humans are not meant to come into contact with the parasite, which infects birds and mammals that live near the water. The parasite thrives in their bloodstreams and releases its eggs in their feces. The eggs then hatch tiny larvae that immediately seek a new host: a specific type of aquatic snail.

Wading in marshy areas along the shoreline could further increase your risk as you creep into snail breeding grounds. The snails host the parasites as they multiply and develop, but eventually they excrete another form of larvae that can cause an allergic reaction in humans.

Other ways to reduce your risk when swimming in potentially infested waters include applying waterproof sunscreen before swimming and rinsing off and toweling dry afterwards, according to the CDC.