Seabather’s Eruption

Seabather’s eruption is lesions found primarily on parts of the body covered by swimwear. The lesions may also appear on your armpits, neck and occasionally on your arms and legs. Most divers and swimmers call it “sea lice.” That term is a misnomer. Sea lice are fish parasites that do not affect humans and have nothing to do with seabather’s eruption, which is caused by the larvae of jellyfish.

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Mechanisms of Injury

The primary offenders in Florida and the Caribbean are the larvae of thimble jellyfish (Linuche unguiculata). These larvae, generally half a millimeter in length, can find their way into bathing suits — even passing through the mesh of some suits — where they become trapped against the skin and will sting. The larvae are visible to the naked eye, but they become nearly invisible in the water. A lack of adult thimble jellyfish in the area is no guarantee that there won’t be larvae. One of the best signs of larvae is the appearance of a rash on swimmers or divers.

The larvae are most prevalent in April through July, although they may appear at any time. The symptoms will appear very soon (24 hours or less) after exposure to the organism and will persist for several days. Some cases record a three- or four-day delay in onset and symptoms lasting several weeks.

Signs and Symptoms

  • Itchy skin eruptions with small blisters and elevated skin areas
  • Fever
  • Headache
  • Chills
  • Nausea and vomiting


  • Wear a wetsuit or impermeable dive skin
  • Avoid t-shirts and one-piece bathing suits, which may trap the larvae
  • Remove your wetsuit, dive skin or bathing suit after diving or swimming in areas with jellyfish larvae
  • Do not shower with your wetsuit, dive skin or bathing suit on (the fresh water may discharge nematocysts)
  • Do not wear the same clothing again without washing — the larvae may remain in the fabric


Many of the symptoms are consistent with other illnesses. Diagnosis can be difficult unless the physician knows of the diver’s exposure to contaminated water. Often the symptoms are very mild, and a physician may consider or diagnose other causes at first. Symptoms can often be severe in children, although adults have also shown severe reactions.

Cases of seabather’s eruption will often clear spontaneously, but others may require treatment. You can consider antihistamines and anti-itching agents, but these are not proven to have significant or consistent results.

Children and individuals with allergies or diseases affecting the immune system may be at risk for severe reactions. Fortunately, the severe reaction is rare, but it can be a danger for some individuals. In these cases, some doctors prefer to use cortisone by tablet or injection.

G. Yancey Mebane, M.D.