You've packed a beach bag and slipped into your swimsuit, and your brain is filled with happy thoughts of fun in the sun. You can't wait to dive into the ocean and feel the saltwater on your skin, right? While that's all great and fun, you’d be wise to remember that basking in the sand and sea presents some risks, too.

One of those dangers? An icky-sounding creature called sea lice—which find their way into beachgoers’ swimsuits and cause a red, bumpy rash called seabather’s eruption.

If you don’t want this to be you, read on for advice to keep yourself rash-free at the beach.

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What exactly are sea lice?

These little guys are not to be confused with head lice. Despite the similar-sounding name, sea lice aren’t anything like those itty-bitty bugs that like to live in your hair and make your head itchy. In fact, they aren’t lice at all, so the name is pretty misleading.

“Sea lice” actually refers to a type of teeny-tiny jellyfish, as well as a particular species of sea anemone. (These are also not to be confused with a parasite called “sea lice” that like to latch onto salmon but don’t affect humans.)

The larval stages of thimble jellyfish and a type of sea anemone called Edwardsiella lineata are so tiny that people don’t even notice when they’re swimming in a pool of them. “These organisms have been described to be the size of a speck of pepper and they’re translucent, making them impossible to avoid in the water,” says Allison Arthur, MD, a board-certified dermatologist in Orlando, Florida.

Jellyfish and sea anemone both release venom when they feel threatened. If you’re just swimming around them, you’ll likely be fine. But these creatures are so small that they can get trapped inside your bathing suit, Dr. Arthur notes. Then, when you get out of the water and plop your tush down onto a beach towel, these critters react and sting you (and, really, who can blame them?).

What’s the most common symptom of sea lice?

If you’ve been stung, you’ll know about 24 hours after you went swimming in the ocean. The venom causes a “hypersensitivity reaction,” Dr. Arthur describes—and the reaction shows up as a bunch of itchy red bumps on your skin. Typically, you’ll see these bumps in areas that were covered by your bathing suit, where the jellyfish or sea anemone larvae were trapped. But some people may also develop a rash in places where friction occurs, like where your thighs rub.

A seabather’s eruption rash typically sticks around for one to two weeks, according to Dr. Arthur. In very rare cases, it can be accompanied by other symptoms like fever, nausea, diarrhea, or headache.

Don’t fret: While it may be annoying, the rash isn’t usually dangerous. Mild cases can be treated with over-the-counter hydrocortisone creams and antihistamine pills, Dr. Arthur says. But she recommends seeing a doctor if you do have symptoms like a fever and headache to make sure you’re not dealing with any other underlying health issue that could be behind your symptoms.

There are some steps you can take to avoid a sea lice problem.

Given that sea lice are basically invisible, it may seem like there’s nothing you can do to protect yourself (other than avoid the ocean!). But even just checking local ocean reports can keep you in the know about sea lice—and you can steer clear of the water if need be.

For instance, thimble jellyfish larvae are rushed into Florida waters and gulf streams in late spring through summer, according to the Florida Department of Health. What’s more, outbreaks of the rash caused by sea lice are reported often in the Caribbean, Mexico, Brazil, the Philippines, and Florida. Rare cases have also popped up in the northeastern US, Dr. Arthur notes.

So, swim at your own risk in these places—and keep an eye out for outbreak reports, she adds. If other people have been reporting rashes after going swimming, there will likely be news stories or messages on community sites and message boards about outbreaks of seabather’s eruption. And, uh, maybe you want to skip the beach that day and have a pool party instead.

If you choose to go swimming anyway, or if there aren’t any reports but you still want to be cautious, bring a change of underwear with you to the beach. You’ll want to change out of your bathing suit as soon as possible, Dr. Arthur says, and rinse your skin using fresh water to get any rogue sea lice off of you. The less chance you give these creatures to sting you, the better.

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When you get home, wash your bathing suit with detergent in the washing machine and then dry it in the dryer if you can. “The heat can help to kill any remaining organisms that are trapped in the fabric,” Dr. Arthur says. She has heard of some cases when a person who got seabather’s eruption after they simply rinsed their bathing suit and let it hang dry. Then, after their first rash had healed, they put their swimsuit on and got the rash again. Not fun.

If you do end up with a sea lice rash, you may want to just toss your suit. “For severe cases of seabather's eruption, you may also consider throwing away the infested bathing suit,” Dr. Arthur says, as the suit might still be carrying itty bitty jellyfish and sea anemone. You don’t really want to chance it.

No matter what, try not to let a fear of sea lice ruin your summer plans. Plenty of people enjoy the beach each year without getting a rash. And if you are unfortunate enough to get stung, you can easily treat the bumps with a little bit of cream from the drugstore.