What Are Sea Lice?
After swimming in warm ocean waters, some bathers discover a red itchy rash on the skin under their bathing suit. Some people call the critters that gave them this rash "sea lice." But they're not lice at all. They're thimble jellyfish larvae.
Real sea lice are parasites that feed on the blood of salmon and other fish. They don't bite humans. For some reason, though, in the 1950s, residents of coastal areas began to call the stings of jellyfish larvae “sea lice bites.” The name just stuck. But that’s not the only name. Some doctors call the skin irritation "seabather's eruption."
The jellyfish larvae that cause this condition float in the ocean. When they swim up under your bathing suit, they get stuck and release stinging toxins. It’s the same thing full-grown jellyfish do, but it hurts a lot less. The toxins trigger your immune system. That’s what causes the bumpy rash. Here are some things you should know before your next jaunt in the ocean.
What Do the Stings Look and Feel Like?
The rash typically appears between 4 and 24 hours after you swim. You might feel a slight prickling sensation in the water when the larvae release their toxins.
You'll often see the rash on areas of your body that your bathing suit covers. You might also find spots on your arms, legs, neck, and in your armpits.
Sea Lice vs. Swimmer's Itch
This rash looks a lot like swimmer's itch. But they're not the same thing. In swimmer's itch, infected snails release tiny parasites into the water. Those critters burrow under your skin and cause an itchy allergic reaction. The rash usually forms on skin that’s outside your bathing suit. And you’ll only get it in freshwater such as lakes.
What Other Symptoms Do They Cause?
In adults, an intensely itchy rash is often the only symptom. Children can have more body-wide symptoms like:
How Long Does the Rash Last?
Usually the rash fades within two weeks. In some people, it can stick around for a few extra weeks.
Are Jellyfish Larvae Toxins Harmful?
Jellyfish larvae toxins aren't dangerous to healthy people. Rarely, children with allergies or a weakened immune system have a more severe reaction. Take your child to the doctor if she has a fever and chills along with the rash.
How Do You Treat the Rash?
Swimmers use a variety of home remedies to relieve the itch of “sea lice,” including rubbing alcohol and meat tenderizer. But there's no evidence these work. Lice treatments won't help either, since it’s not really lice you’re dealing with.
An antihistamine pill or steroid cream can help relieve the itch. If you have a more severe case, your doctor may prescribe a steroid pill or shot. You can also apply colloidal oatmeal cream or calamine lotion to soothe the itch while the rash heals.
How to Avoid the Rash
The only way to avoid stings is to stay out of the water during peak season. Use caution if you swim or dive along the coast of Florida or the Caribbean between May and August. That’s when jellyfish release their larvae into the water.
Even the best precautions when you swim in these areas may not protect you. Jellyfish larvae are as small as specks of black pepper, and just as hard to see when they float in the ocean. And you may not see any larger adult jellyfish nearby.
Protect yourself when you dive by wearing a wetsuit. Don't wear a t-shirt or one-piece bathing suit into the ocean, because it can trap the larvae inside. Bathing suits made from tightly woven fabrics are better at keeping out jellyfish larvae than loosely woven fabrics.
Remove your wetsuit or bathing suit when you get out of the water, and rinse off in the shower. The more exposure you have to the jellyfish larvae toxins, the worse the rash will get. Wash your bathing suit in hot water and put it in the dryer to kill any larvae trapped in the fabric.
Alaska Department of Fish and Game: "What Are Sea Lice?"
CDC: "Swimmer's Itch FAQs."
Divers Alert Network: "Debunking the Sea Lice Myth."
Florida Department of Health: "Sea Lice or Seabather’s Eruption."
Medscape: "Seabather's Eruption."
StatPearls: "Seabather’s Eruption."