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Seabather's eruption in Adult
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Seabather's eruption in Adult

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Contributors: Robert Norris MD, Joanne Feldman MD, MS
Other Resources UpToDate PubMed


Seabather's eruption is caused by envenomation by and subsequent hypersensitivity to the larval form of marine coelenterates encountered in seawater. Larvae of the thimble jellyfish, Linuche unguiculata, are the cause of eruptions in the Atlantic Ocean off the coastline of Florida, Mexico, and the Caribbean. The adult size is 5-20 mm (up to 3/4 inch), and the larval form is only 0.5 mm. Off the coast of Long Island, NY, sea anemone larvae of Edwardsiella lineata have also been identified as causal. Most cases occur between March and August. 

Some refer to seabather's eruption as "sea lice," although this is a misnomer, as true sea lice are skin parasites of fish that do not affect humans.

Envenomation occurs when the larvae get caught beneath swimwear and stinging cells (nematocysts) discharge into the skin. The mechanical pressure of swimwear is hypothesized to, in part, trigger the firing of these cysts.

Patients present minutes to days after emerging from seawater with a pruritic, papular rash in the distribution of their bathing suit or other areas of pressure including surfboard contact. Symptoms usually persist for 5-7 days. Some patients may develop fever, headache, malaise, and emesis (especially children). Conjunctivitis and urethritis may develop if exposure to those mucous membranes occurs. Systemic hypersensitivity reactions, including anaphylaxis, are rare in jellyfish envenomations. Rarely the rash may recur within 2 weeks, and atopic individuals may have lesions for up to 6 weeks.

Risk factors include being less than 16 years of age, a past history of seabather's eruption, and surfing. Showering without a bathing suit after seawater exposure has been found to be protective. Having a history of seabather's eruption increases the risk of future episodes, which supports the theory that this condition is due to underlying hypersensitivity. Some individuals are apparently immune, however, and do not develop a rash despite similar, repeated exposures in the same seawater as those who are symptomatic. No deaths have been reported.


T63.691A – Toxic effect of contact with other venomous marine animals, accidental, initial encounter

238534006 – Sea bather's eruption

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Differential Diagnosis & Pitfalls

  • Patients with "swimmer's itch" (animal schistosomes) have lesions outside the bathing suit area.
  • Seaweed dermatitis is more severe and leads to blistering and desquamation; it is also endemic to Hawaii where seabather's eruption has not been reported.
  • "Dogger bank itch" (Bryozoa dermatitis) is an algae-induced seaweed dermatitis. This condition is found in dockworkers along the North Sea and the Mediterranean. The lesions are chronic and can be disabling.
  • Other ocean-dwelling organisms (hydromedusae, crab larvae)
  • Varicella
  • Scabies
  • Contact dermatitis
  • Folliculitis
  • Insect bites
  • Urticaria
  • Pseudomonas folliculitis
  • Schistosomiasis

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Last Updated: 10/03/2017
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Seabather's eruption in Adult
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Seabather's eruption : Rash, Non-traumatic saltwater exposure, Primarily truncal, Ocean swimming
Clinical image of Seabather's eruption
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