Seabather's Eruption Symptoms and Treatment

The Full Story

When tiny jellyfish larvae get trapped between the skin and swimming garments, they can cause a burning, itching rash that can make you feel like your skin is on fire under your bathing suit. 

Small juvenile jellyfish (larvae) float near the surface of seawater where they can easily be encountered by swimmers. They are small enough that they often cannot be seen and easily get stuck between the skin and bathing garments. When this happens, they can discharge their nematocysts (part of the tentacles that release venom), essentially causing a jellyfish sting under the swimsuit.

Because the larvae are so small, many swimmers do not initially feel a sting but can develop a hypersensitivity (allergic reaction) to either the larvae itself or the venom released. Some people have symptoms before leaving the water but symptoms can also be delayed for up to 24 hours. Seabather’s eruption is characterized by a red, itchy, raised rash in areas covered by swimming garments. 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. Individuals affected by seabather’s eruption might feel a burning sensation and the rash may continue to spread over the next few days. The rash of seabather’s eruption is different than the rash associated with swimmer’s itch, as swimmer’s itch affects uncovered areas of the body. Seabather’s eruption occurs in tropical waters as well as the southern and eastern coastal areas of the United States. 

While seabather’s eruption is very uncomfortable, it generally does not cause symptoms of anaphylaxis (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 more common in children than adults.

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. Topical application of vinegar may help prevent further nematocyst discharge. The rash can be treated with topical steroids such as hydrocortisone cream and antihistamines such as diphenhydramine (Benadryl®). Avoid excessive scratching because this can lead to a skin infection. Those with gastrointestinal symptoms such as diarrhea should try to keep well hydrated. Most cases of seabather’s eruption will 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 larvae again. 

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