What You Should Know About Sea Lice

If you’re headed to the beach, you’ve probably thought about the essentials — sunscreen to prevent burns, a big umbrella for shade, and plenty of water and snacks. But here’s one thing you might not have planned for: sea lice.

They may sound like mythological creatures, but sea lice (or sea louse) are real. They’re tiny saltwater larvae that can cause an itchy rash.

Internal medicine physician Meghan Galili, MD, shares how to spot and treat sea lice rash and offers advice to keep those little critters from stinging you.

What are sea lice?

Sea lice are larvae from certain jellyfish and sea anemones that live in saltwater oceans and seas. They’re most commonly reported in Florida and the Caribbean between March and August, peaking in May and June.

“Sea lice can be unpredictable because they drift with the currents,” Dr. Galili says. “A beach that had sea lice one year may not have them the next, and vice versa.”

Despite the name, sea lice aren’t like head lice. But they’re about the same size (2 to 3 millimeters, about the size of a sesame seed). Because they’re so small and nearly see-through, sea lice are almost impossible to see with the naked eye.

Unlike head lice, which bite and burrow into your scalp to feed on your blood, sea lice can sting. And those stings can cause a rash called seabather’s eruption. It can appear within minutes or up to a day after exposure. 

“If the larvae get pressed against your skin or trapped in your swimwear, they can release a stinging toxin as a defense,” Dr. Galili explains. “Seabather’s eruption is an allergic reaction to those toxins.”

What a sea lice rash (seabather’s eruption) looks like

Although seabather’s eruption can be uncomfortable, it’s usually not a serious concern. It’s typically easy to spot and treat. A sea lice rash is usually:

• Very itchy
• Red and raised
• Similar in appearance to small pimples, blisters or welts

One of the biggest clues is where the rash appears. “A sea lice rash tends to affect areas covered by your bathing suit, like your chest, abdomen, butt or groin,” Dr. Galili says.

Sea lice can also get caught in hair on your head or body. While most cases are mild, some people may experience whole-body symptoms, like:

• Abdominal pain
• Diarrhea
• Fever
• Malaise (a general feeling of illness)
• Nausea and vomiting

Severe allergic reactions, like anaphylaxis, are rare, even in people who have other allergies.

Seabather’s eruption can affect people of any age, but children often experience stronger symptoms. And if you’ve had seabather’s eruption before, you may react differently next time. In some cases, the rash can become more intense after you get it a second or third time.

Treating sea lice rash

Treating seabather’s eruption focuses on calming itching and inflammation.

Mild cases of seabather’s eruption can be treated at home with remedies like:

• Antihistamines
• Hydrocortisone cream
• Applying a cold pack (wrapped in a cloth) for up to 15 minutes

And tough as it may be, try to avoid scratching the rash. Scratching could damage your skin or cause an infection. “If your child can’t keep their hands away, consider having them wear soft gloves until the rash improves,” Dr. Galili suggests.

In some cases, a healthcare provider may prescribe stronger anti-itch medications, particularly if the rash affects sensitive areas like your face, groin or armpits.

“These areas tend to be more sensitive and more prone to severe inflammation and itching,” she adds.

Most sea lice rashes improve within about two weeks, though more severe reactions may take up to a month to fully clear.

If you notice possible signs of infection — like pus, increasing redness, swelling, warmth, fever or worsening pain — contact a healthcare provider.

How to prevent a sea lice rash

You can’t always avoid sea lice, but a few precautions may lower your risk of developing a rash.

• Check beach health reports. Local health departments sometimes issue notices if sea lice are present. If you see an advisory, it may be best to avoid swimming in that area.
• Pay attention to early symptoms. A tingling sensation under your swimsuit while swimming may be an early sign of sea lice. Get out of the water and out of your swimsuit ASAP.
• Remove swimwear and rinse off. Take off your swimsuit and rinse your body with unaffected salt water, if possible. Freshwater can sometimes trigger trapped larvae to release toxins, so removing your swimwear before showering is important.
• Wash your swimsuit thoroughly. Always wash swimwear before wearing it again. Letting it dry and rewearing it without washing may leave lingering larvae behind.
• Consider vinegar after swimming. Applying vinegar containing 5% acetic acid to your skin after swimming may help deactivate some larvae before they release toxins.

Fortunately, seabather’s eruption is usually more irritating than dangerous. Preparing for the elements and cleaning yourself and your swimwear and gear after a dip in the water can make all the difference.

“If you plan to swim in potentially affected areas, take a few precautions first,” Dr. Galili advises. “Choose a beach where you have access to a place to change and shower after swimming. That way, you can focus on enjoying the water instead of dealing with an itchy rash.”