Sea lice is skin irritation due to the trapping of small jellyfish larvae underneath bathing suits in the ocean. Pressure on the larvae causes them to release inflammatory, stinging cells that cause itching, irritation, and red bumps on the skin. Doctors also call this sea bather’s eruption or pica-pica, which means “itchy-itchy” in Spanish.

Although they’re called sea lice, these larvae have no relation to the lice that cause head lice. They aren’t even sea lice — actual sea lice only bite fish. However, the term has stuck over time.

While the skin irritation is usually mild to moderate, some people can experience more severe side effects, such as a high fever in children. While the sea lice bites were first identified in areas of the southern coast of Florida, they also have been identified in tropical and subtropical areas around the world. Outbreaks are usually worse from March to August.

You can experience the symptoms of sea lice bites almost immediately after getting in the water. You may describe the initial symptoms as “prickling” sensations. After this time, the skin will usually start to itch. Additional symptoms may include:

  • headaches
  • lethargy
  • nausea
  • rash that appears underneath where a bathing suit would be
  • red bumps that may come together and resemble a large, red mass

The jellyfish larvae also have a particular liking for hair, which is why many people may find the bites begin on the back of their necks. However, it should be emphasized that even though they may cling to hair, they’re not head lice.

The rash usually lasts about two to four days. However, some people may experience a rash from sea lice bites for up to two weeks. Children are especially prone to experience severe symptoms associated with sea lice bites, including nausea and high fevers.

Sea bather’s eruption usually occurs during warm summer months when winds bring thimble jellyfish and anemone larvae near the shoreline. Sea lice bites seem to be especially common in Palm Beach and Broward counties in Florida where Gulf Stream winds blow currents.

When you swim in the ocean, the larvae become trapped inside your swimsuit. The larvae have stinging cells known as nematocysts. When the larvae rub against your skin, you experience the skin irritation known as sea lice bites.

Wearing tight bathing suits makes the bites worse because of the added friction. So, does rubbing a towel against the skin.

You can also get sea lice bites if you put a swimsuit back on that you haven’t washed or dried. Because the stinging cells aren’t alive, they can stay on clothing.

You can usually treat sea lice bites with over-the-counter treatments. Examples include applying 1 percent hydrocortisone cream to areas of the bites two to three times a day for one to two weeks. This can help to reduce itching and inflammation. Other steps you can take include:

  • applying diluted vinegar or rubbing alcohol to irritated areas to soothe them
  • applying cloth-covered ice packs to the affected areas
  • taking nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and aspirin, to reduce pain and inflammation (however, children under age 18 shouldn’t take aspirin)

Sometimes, a person can have a severe reaction to sea lice bites and need to seek medical attention. A doctor may prescribe oral corticosteroids, such as prednisone.

With treatment, sea lice bite symptoms will go away within four days.

Sea lice bites aren’t contagious. Once you have the sea lice bites rash, you can’t pass it along to another person.

However, it’s possible that if you loan out your swimsuit without washing it, another person could get a rash from the cells. This is why you should wash your swimsuit and dry it in warm heat after washing.

If the stinging jellyfish larvae are present in the ocean, there’s little you can do to prevent getting bitten other than staying out of the water. Some people have tried to apply barrier creams to the skin or wear wet suits to avoid the bites. However, most people are still affected.

Doctors do know that swimmers and snorkelers are more vulnerable to the effects of sea lice bites because the jellyfish seem to live on the surface of the water.

Pay attention to lifeguard stations and warnings before getting in the ocean. Beaches will often issue warnings if sea lice infestations are affecting people.

Also, change your swimsuit quickly after getting out of the water. Wash your skin in seawater that is known to not have jellyfish larvae present. (Washing the skin in freshwater or vinegar immediately after leaving the water can make the bites worse.)

Gently pat your skin dry (don’t rub) and wash all bathing suits after wearing.

Sea lice bites can range from a nuisance in adults to the cause of nausea, fever, and more severe symptoms in children. While the rash typically goes away with time and isn’t contagious, you may wish to try over-the-counter treatments, like hydrocortisone creams, to reduce itching. If that doesn’t work, check out these other great remedies for itching.