Sea lice, which doctors may call seabather’s eruption, refers to an itchy skin reaction that occurs after a person swims in the ocean. However, “sea lice” is a misnomer. The actual cause involves small jellyfish and sea anemones.

These tiny animals become trapped between swimwear and the skin while a person is in the sea. The creatures release cells when under pressure that sting the person’s skin, causing irritation and itchiness.

This article reviews what seabather’s eruption is, its symptoms, causes, risk factors, treatment, and prevention.

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Sea lice refers skin irritation and itchiness following swimming in the ocean. The name is a misnomer (inaccurate term), so many people refer to it as “seabather’s eruption” instead. The underlying cause does not involve insects.

Instead, small jellyfish and anemones become trapped in a person’s swimwear during activities in the sea. The creatures release toxins due to pressure, friction, or exposure to freshwater when a person leaves the ocean.

The toxins cause symptoms to occur when they enter someone’s skin. The immune system reacts and causes localized inflammation. A person will then often experience extreme itchiness and a burning sensation, according to older research from 2015.

Seabather’s eruption is relatively common and can affect anyone who goes into the ocean. However, it often occurs in warm waters off the United States, such as the Gulf of Mexico, and other geographic areas around the world.

The most prominent symptom involves intensely itchy and stinging skin. The symptoms may start in the water, after drying off, or when rinsing in freshwater.

Small papules, or bumps, may appear where bathing attire came in contact with a person’s skin. A rash may appear on other areas of the skin as well.

People who shower while wearing their swim attire may notice increased symptoms, since the creatures respond to contact with freshwater.

In rare cases, a person may develop additional symptoms, such as:

The underlying cause of seabather’s eruption involves two small organisms: a thimble jellyfish (Linuche unguiculata) and a sea anemone (Edwardsiella lineata). These creatures can become trapped between the swimmer’s skin and the fabric of their swimwear.

When put under pressure or friction or when exposed to freshwater, the creatures release an organ that scientists call “nemocytes.” This organ releases various toxins.

Researchers believe that the jellyfish may cause seabather’s eruption at any stage of their life cycle.

A person’s immune system reacts to the stings and toxins, causing itchiness and inflammation. Small, discolored papules may occur on the skin where the bathing attire came in contact with the skin.

Who is at risk?

Anyone who goes into the ocean can come in contact with the sea creatures that cause this reaction. Some coastal areas where a person may experience exposure to these sea creatures more commonly include:

  • the Gulf of Mexico
  • the Caribbean
  • the southeast coast of the U.S., which may include Florida, the Bahamas, and Cuba

A person may also develop the condition in other geographic areas. For example, the City of New York warns that cases of seabather’s eruption may occur when people swim in the water off of Long Island.

People have a higher risk of coming in contact with the creatures responsible for the eruption in May and June.

Individuals who may be more likely to experience the condition include:

  • surfers
  • children ages 15 years or younger
  • people with a history of seabather’s eruption

Researchers suggest that children may have a higher risk of experiencing the condition than adults because they tend to spend more time in the water and may have more sensitive skin.

Older research suggests that, in most cases, seabather’s eruption will clear within 1–2 weeks without medical treatment. However, another older source suggests that it can last up to 2 months.

Doctors may provide treatment for the symptoms a person develops. Often, this involves oral antihistamines, topical steroids, or a combination of both.

Doctors may suggest the use of second-generation antihistamines for daytime hours, such as fexofenadine. These medications are less likely to cause drowsiness than first-generation antihistamines.

For nighttime, they may recommend a person use diphenhydramine, which is a first-generation antihistamine. Diphenhydramine may cause drowsiness and may help someone sleep despite the intense itching.

The type of steroid cream a doctor recommends can vary based on the location of the rash. When it appears on areas such as the torso, legs, or arms, they will likely prescribe high potency corticosteroids, such as clobetasol.

For sensitive areas, a doctor may prescribe less potent topical steroids, such as hydrocortisone. Sensitive areas include the groin, face, and armpits.

A person can avoid seabather’s eruption by not swimming in the ocean or sea. Otherwise, there is no way to prevent the condition from occurring.

Removing swimwear and showering after coming out of the water may lessen the severity of the eruption but is unlikely to prevent it from occurring.

A person should also wash all swimwear in water with detergent before wearing it again. Otherwise, the sea creatures that cause seabather’s eruption can remain on the clothing even after it dries and may cause another skin reaction when a person puts them on.

Sea lice refers to an itchy rash that appears on a person’s skin either while they are in seawater or shortly after leaving it.

Tiny jellyfish and sea anemones cause the reaction, rather than lice. These creatures can become trapped in the fabric of swimwear and cause a reaction either due to friction, pressure, or exposure to freshwater.

The condition can affect anyone, but it commonly occurs in warm waters where the sea creatures that cause it live.

The rash typically clears within a few days to 2 weeks without intervention. However, a healthcare professional may provide treatments to help alleviate symptoms, such as antihistamines and topical steroids.

The only way a person can completely prevent sea lice is by not going into the sea.