The Hidden Sting: How Seabather’s Eruption Can Spoil Your Swim

What is seabather’s eruption?

Small juvenile jellyfish (larvae) float near the surface of seawater, where they can easily be encountered by swimmers. They are so small that they often cannot be seen. They easily get stuck between the skin and a swimsuit. When this happens, they can discharge their nematocysts (part of the tentacles that release venom), essentially causing a jellyfish sting under the swimsuit. Seabather’s eruption is often referred to by the name “sea lice,” but this term is incorrect. Sea lice are fish parasites that are unrelated to seabather’s eruption.

What does seabather’s eruption look like?

Seabather’s eruption is characterized by a red, itchy, raised rash in areas covered by swimsuits. 

What are the symptoms of seabather’s eruption?

Because the jellyfish larvae are so small, many swimmers do not initially feel a sting, but can develop a hypersensitivity (allergic reaction) to either the larvae themselves or the venom release. Some people have symptoms before leaving the water, but symptoms can be delayed for up to 24 hours. 

People affected by seabather’s eruption might feel a burning sensation, and the rash can continue to spread over the next few days. The rash of seabather’s eruption is different from the rash associated with swimmer’s itch, as swimmer’s itch affects uncovered areas of the body. Seabather’s eruption can occur in tropical waters, as well as in the southern and eastern coastal areas of the US. 

Is seabather’s eruption dangerous?

While seabather’s eruption is very uncomfortable, it generally does not cause symptoms of anaphylaxis (a severe allergic reaction), such as trouble breathing or facial swelling. In most cases, the only symptom is a rash. Occasionally, other symptoms such as fever, fatigue, sore throat, and abdominal discomfort can occur. These symptoms tend to be more common in children than adults.

Can seabather’s eruption spread? Is it contagious?

Seabather’s eruption is unlikely to spread directly from person-to-person unless unwashed swimsuits are shared. If more than one person in a group is affected, it is usually due to them having been exposed while in the same body of water.

How do you treat seabather’s eruption?

Most cases of seabather’s eruption can be easily treated at home. If you suspect seabather’s eruption, remove any bathing garments as soon as possible. Applying vinegar to the skin might help prevent further nematocyst discharge. The rash can be treated with topical steroids such as hydrocortisone cream and antihistamines such as diphenhydramine (Benadryl). Avoid scratching the affected area, as this can lead to a skin infection. Those with gastrointestinal symptoms such as diarrhea should try to stay well hydrated. Most cases of seabather’s eruption resolve within 1 to 2 weeks. It is important to know that if you have had seabather’s eruption in the past, you are more likely to have a reaction if you are exposed to the larvae again. 

If you suspect that someone has seabather’s eruption or if you have a question about seabather’s eruption, help from experts is available through the webPOISONCONTROL online tool and by phone at 1-800-222-1222. Poison Control’s expert guidance is always free, confidential, and available 24 hours a day.

Maryann Amirshahi, PharmD, MD, MPH, PhD
Medical Toxicologist

Revised William G. Troutman, PharmD
Professor of Pharmacy Emeritus 

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