The rash is called swimmer’s itch, or cercarial dermatitis, and it’s actually a pretty common occurrence in the summer across the US and around the world. It can happen anywhere people frequently swim, either fresh or saltwater, with the right combination of conditions. It’s also sometimes known as clam-digger’s itch or duck itch.
The parasites that cause swimmer’s itch are called cercariae, and they naturally live in the blood of animals such as ducks, geese, swans, and raccoons that live in or around lakes, ponds, and oceans. The parasites produce eggs that are then released via the animals’ feces.
Tiny larvae, which tend to congregate in shallow waters by shorelines, hatch from these eggs and instantly look for their next host: a specific species of aquatic snail.
The snails, once infected, release their own larvae that can infect people by burrowing into their skin. Since humans are not the normal host — they prefer to invade birds or nonhuman mammals’ bodies — this is the end of the parasites’ life cycle and they soon die. But not before triggering an incredibly annoying and itchy allergic reaction.
But why do some people develop swimmer’s itch while others who spend time in the same waters don’t? It simply comes down to a person’s own sensitivity to the parasitic infection, Brent Bellinger, a senior environmental scientist overseeing the lakes in Austin, told BuzzFeed News.
Because it’s an allergic reaction, not everyone who encounters or is attacked by the larvae will develop a rash. It takes repeated exposure to the tiny parasites before your immune system recognizes the invaders, setting off the reaction.
If you’ve encountered the larvae before, a rash can appear within minutes to days after swimming in contaminated water.
Caussey, who also posted about her experience on TikTok, said hundreds of other people were swimming in the lake with her, including employees who stood in the water to help people with their rentals. “It was weird. Everyone on TikTok was like, ‘you’re not supposed to swim in there’ and all this stuff, but there were so many people.”
A spokesperson for the Austin water rental company Live Love Paddle, which services Lady Bird Lake, told BuzzFeed News that the call was the company’s first time hearing about swimmer’s itch. They said anywhere between 50 to 100 people will visit the lake to enjoy the water during the week, and about 300 on busy weekends.
There are no signs at the lake currently warning of the parasite’s presence, but the spokesperson said they will post one if they find it to be an issue.
Bellinger said swimmer’s itch is unfortunate, but “really not a big deal” for most people. Itchiness tends to fade after about a week, which Caussey can speak to, without any risks of serious health consequences. (She called her doctor, who prescribed inflammation-fighting corticosteroid pills for a week — and who told her his daughter developed the same rash after swimming in a local Texas pond a couple of weeks prior.)
Importantly, Bellinger said it’s still safe to swim in natural bodies of water this summer, including Lady Bird Lake — you just have to acknowledge that a multitude of things can happen while interacting with nature. (This parasite generally isn’t an issue in chlorinated pools.)
”I appreciate that these people posted about swimmer’s itch so people don’t overreact when they get these types of rashes and can pay better attention to what’s going on and just be more informed about the environment,” Bellinger said, adding that he’s more concerned about getting an ear infection after swimming in natural waters. “It’s just about being smart and taking those extra precautions when you get out of the water.”
How to reduce your risk of swimmer’s itch
To reduce your chances of developing swimmer’s itch, you can try these CDC tips:
Try to towel dry or shower immediately after swimming.Avoid swimming in waters where signs say it’s unsafe.Don’t feed birds or do other things that attract waterfowl to swimming areas.Don’t swim in shallow or marshy areas where snails are commonly found.
Some people on social media say rubbing baby oil on their skin before swimming has saved them from swimmer’s itch. This may help because it adds a thick fatty layer on the skin that prevents the parasites from burrowing, Bellinger said. But he advises against this because some products could harm aquatic life.
A layer of sunscreen or clothes on top of a bathing suit could likely also do the trick, though there is no official way to prevent infection or reaction.
There’s also no telling how common swimmer’s itch actually is. Local public health departments are not required to report cases to the CDC, an agency spokesperson told us, and little research has been done on the reaction. The Texas Department of State Health Services told BuzzFeed News that swimmer’s itch isn’t a “notifiable condition” in the state, so cases would not be reported.
“In my opinion, it’s something that’s shrugged and accepted as what occurs when you swim in a natural water body because it’s relatively short-lived and benign,” Bellinger said.
Little is known about how climate change is affecting the prevalence of these parasites, too, Bellinger said. However, warmer conditions can lead to higher concentrations of cercariae, according to a 2004 study published in the American Journal of Public Health. So hotter summers or bodies of water in southern regions may be more likely to encourage the growth of the parasite.
Here are some other important facts to know about swimmer’s itch:
Most cases do not require medical attention and can be relieved with corticosteroid creams, baths in Epsom salt or baking soda, and cool compresses to affected areas. The CDC recommends mixing baking soda with water to form a paste and applying it to the skin.It’s not contagious.There’s no way to know beforehand whether water is contaminated, so be sure to towel dry and shower immediately to prevent irritation after swimming.There’s no official test to diagnose it and skin biopsies are not helpful.Scratching your rash may cause a secondary bacterial infection, so try to avoid itching for at least a week.Swimmer’s itch can look like other conditions, including impetigo, chickenpox, poison ivy, and herpes.
“The chances of having any kind of adverse reaction is pretty small,” Bellinger said, “but it’s important to follow best practices.”