What Are Sea Lice, and How Do You Avoid Their Red, Itchy Rash?

While the rash isn't usually a serious health concern, it can be irritating.

When a purple warning flag flies at Florida beaches it indicated dangerous marine wildlife present in the water. Of course, our first thought goes to sharks or jellyfish, but there's a smaller marine creature that can also raise the purple flag—the sea lice. The good news is: The tiny animals are more of a nuisance than a danger. Still, here's what you should know about sea lice stings symptoms and prevention.

Florida beachgoers have been warned about stinging sea lice that cause an irritating, red rash. The rash is also known as swimmer's itch. So what are sea lice exactly, and how concerned should you be about going to the beach? That depends on where, exactly, you're headed. 

They're Actually Jellyfish and Sea Anemone

Residents who suffered strange rashes after swimming in coastal water inappropriately coined the term "sea lice" during the 1950s. It turns out there is such a thing as actual sea lice. But they are tiny parasites that affect fish, not humans. 

The rash humans tend to get, on the other hand, is caused by two species: Thimble jellyfish and a sea anemone. Those fish are small enough to become trapped underneath bathing suits, typically where the rash is found. 

The combination of pressure and freshwater causes the organisms to produce a stinging organ called nemocytes, which release toxins. Those toxins then cause an immune response in the form of a rash.

Sea lice are in no way related to head lice, which are contagious parasites that live on people's heads and are common among young children.

Sea Lice Are Common Throughout Florida

The rash associated with sea lice—also known as sea bather's eruption—has been documented along Florida's coastline for several decades, according to the Florida Department of Health. 

Complaints tend to peak from March through August, and outbreaks appear to be caused by shifts in ocean currents since that can bring the larvae closer to the shore. According to the Florida Department of Health, the hardest hit areas are in the southern part of the state—in Palm Beach and North Broward counties—where the Gulf Stream passes closest to the shore.

Because most people treat themselves, there aren't any good estimates of how prevalent the rashes are. 

Sting Symptoms and Treatment

The most common symptom of a sea lice attack is a red, itchy rash on the skin, typically in areas underneath a bathing suit. According to StatPearls, some people have felt stinging upon their skin after leaving the water. The rash usually lasts for two weeks but has been reported to last longer than one month.

Some people can experience more serious reactions to the larvae stings, including fever, vomiting, nausea, and cramps. According to StatPearls, those symptoms usually last less than a week. And fortunately, the symptoms aren't serious for most people who get stung. 

"They aren't very intense, which is why we call them sea lice and not sea hornets or sea wasps," Dave Greenwood, director of public safety for Pensacola Beach, told the Pensacola News Journal.

Itching and irritation can be treated with an over-the-counter (OTC) 0.5% hydrocortisone skin cream, according to the Florida Department of Health. An oral antihistamine (like Benadryl) may help, as well.

How To Protect Yourself

First and foremost, check lifeguard postings for water safety information before swimming at a public beach. Also, don't go in the water if sea lice have been detected. That's especially true if you've had sea lice rash, which may make you more vulnerable to another reaction, according to the Florida Department of Health.

Swimmers can also reduce their risk of getting stung by sea lice by wearing sunscreen, which may protect the skin from penetration by the larvae. Also, by not wearing a t-shirt in the water, larvae won't be able to get stuck between clothing and skin, according to the Florida Department of Health.

It's also important to shower immediately after swimming and wash your bathing suit after wearing it, according to the Florida Department of Health. 

Additionally, there's some evidence that re-wearing a bathing suit that has been air-dried can trigger a rash recurrence. So, wash your bathing suit with detergent and dry it with heat if you know you've been exposed to sea lice.

A Quick Review

Sea lice—unrelated to head lice—have been occupying Florida beaches and causing red, itchy rashes in people who swim there.

While these organisms are not super dangerous, they can cause an irritating rash. If you are swimming on Florida beaches, pay attention to lifeguard postings and avoid the ocean if sea lice are detected.

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  1. Tomchik RS, Russell MT, Szmant AM, Black NA. Clinical perspectives on seabather’s eruption, also known as “sea lice.” JAMA. 1993;269(13):1669-1672.

  2.  Florida Department of Health. Sea lice or seabathers eruption.

  3. Prohaska J, Jamal Z, Tanner LS. Seabathers eruption. In: StatPearls. StatPearls Publishing.

  4. MedlinePlus. Head lice also called pediculosis.

  5. Florida Department of Health Palm Beach County. Sea lice.

  6. Pensacola News Journal. Stinging sea lice lead to purple flags at Pensacola Beach.

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