Sea lice rash can appear as many small, itchy bumps or larger hives on areas of skin covered by a bathing suit or a person’s hair, such as the back of the neck.

More formally known as seabather’s eruption (SBE), sea lice rash results from swimming in tropical or subtropical sea water containing certain tiny jellyfish and anemones.

This article discusses sea lice rash, its symptoms, treatment, duration, when to consult a doctor, and frequently asked questions.

This section examines some photographs of sea lice rash or SBE.

The marine creatures that cause sea lice rash are not actually lice.

They are the thimble jellyfish Linuche unguiculata at its free-swimming stages of development: its larvae, medusae, and ephyrae.

These are present in the West Atlantic Ocean, which includes the Caribbean, Florida, and Mexico.

However, experts have also reported the rash in the Long Island area of New York State due to the larval stage of the sea anemone, Edwardsiella lineata.

Due to their small size, the jellyfish and anemones can easily become trapped between bathing suit fabric and a person’s skin.

Although they do not have physical stingers, they release stinging cells that contain toxins.

Pressure on the organisms from the bathing suit causes the stinging cells to discharge, releasing toxins into the skin. This triggers the body’s immune system, which reacts with the sea lice rash.

The stinging cells can also discharge when a person rinses with fresh water, or over time as the water evaporates.

Therefore, wearing bathing suits for prolonged periods after swimming, showering in fresh water, and rubbing the skin with a towel can worsen the eruption.

The jellyfish and anemones can also accumulate in the hair and sometimes cause SBE on the back of the person’s neck.

Some people with sea lice rash notice a prickling sensation while still in the water, typically in the tight-fitting areas of their swimsuits.

Usually, symptoms appear several hours after the person has left the water.

Symptoms typically include a prickling sensation, itchiness, and bumps or hives on the skin.

In a severe reaction, a person may experience:

People under 15 years old may experience more symptoms than adults, partially because they spend more time in the water.

Also at risk for more pronounced symptoms are surfers and people who have experienced SBE in the past.

Most cases of sea lice rash resolve with at-home care.

Sea lice rash treatment includes:

  • 5% acetic acid to inactivate any undischarged stinging cells
  • rubbing alcohol or diluted vinegar to neutralize any remaining toxins
  • an ice pack to ease any pain
  • antihistamines and topical corticosteroids to reduce inflammation
  • antihistamines to ease itching
  • topical calamine and menthol lotion to help reduce the itch
  • nonsteroidal anti-inflammatory drugs for pain and inflammation — note that children should not have aspirin

Anyone experiencing sea lice rash should also ensure they wash their bathing suit in hot, soapy water and rinse it in vinegar or alcohol, followed by a heated dryer cycle to remove any remaining stinging cells.

People experiencing severe reactions or signs of infection should consult a doctor.

Signs of infection include:

  • swelling
  • increased pain
  • warmth
  • redness or red streaks on lighter skin
  • pus

The following section covers common questions about sea lice rash.

How long does sea lice rash last?

Sea lice rash usually lasts 1–2 weeks but may persist for up to 2 months.

Can sea lice rash spread?

A sea lice rash may continue to spread on the affected person for a few days after their initial exposure.

It is not transmissible and can not pass to another person unless they borrow swimwear that still contains some stinging cells.

Can a person avoid sea lice?

The only way to ensure that a person does not get sea lice rash is to stay out of water that contains the rash-causing jellyfish and anemones.

According to Florida Health, these organisms are likely to be present during summer, and the peak months for sea lice issues in Florida are March–August.

Sea lice rash is an immune system response to the sting toxins from small jellyfish and sea anemones. The small sea creatures release stinging cells when they become trapped by a person’s bathing suit fabric.

The rash can last several weeks and may cause other symptoms such as headaches, nausea, and fever. People who experience severe reactions or signs of infection should contact a doctor.