The Dermatologic Perils of Swimming: Seabather’s Eruption

August 2, 2004
Mary L. Sy, MD
Mary L. Sy, MD

,
Gary P. Williams, MD
Gary P. Williams, MD

This 10-year-old boy presented forevaluation of a rash that developedduring a spring vacation on Florida’sAtlantic coast. After he had beenswimming in the ocean, a pruritic,erythematous, papular rash developedon his trunk, axillae, and groin. Approximately24 hours after the onsetof the rash, he experienced malaise,chills, and a sore throat. His past medicalhistory was unremarkable. Hehad been fully immunized and hadhad varicella infection.

This 10-year-old boy presented forevaluation of a rash that developedduring a spring vacation on Florida'sAtlantic coast. After he had beenswimming in the ocean, a pruritic,erythematous, papular rash developedon his trunk, axillae, and groin. Approximately24 hours after the onsetof the rash, he experienced malaise,chills, and a sore throat. His past medicalhistory was unremarkable. Hehad been fully immunized and hadhad varicella infection.This boy has seabather's eruption,a pruritic dermatitis that occursafter exposure to seawater that containscertain species of jellyfish--particularlythe larval form of the thimblejellyfish (Linuche unguiculata). Thelarvae are found in seawater in areaswhere this eruption is endemic, suchas the Caribbean and the Atlanticcoast of Florida, where this boy hadvacationed. The jellyfish are foundin these warm waters from Marchthrough August, with peak concentrationsin May and June. The first writtenreports of this disease came fromFlorida's Delray Beach.The jellyfish larvae containvenom-filled barbs that fire theirvenom into the skin when the larvaebecome trapped under a bathing suit.Changes in osmotic pressure, suchas air-drying or showering with freshwater, also trigger the barb-firing process.The venom causes a local toxicreaction and can precipitate a systemichypersensitivity reaction. Thelocal reaction--an erythematous, pruritic,papular dermatitis--may beespecially heavy on the skin underthe bathing suit and in areas coveredwith hair, such as the axillae. It appears4 to 48 hours after exposure toinfested seawater. Systemic symptomsare more common in childrenthan adults and include malaise, fever,sore throat, abdominal pain, headache,cough, and diarrhea.Both the rash and systemicsymptoms generally resolve in 1 to 2weeks. Treatment is supportive andincludes antihistamines and topicalcorticosteroids. Systemic corticosteroidsare reserved for severe cases.The best preventive measure is toavoid swimming in infested water altogether.Those who choose to swimin potentially infested waters need tobe aware that the wearing of T-shirtsfor ultraviolet protection increasesthe risk of getting seabather's eruption.Bathers should instead use awaterproof sunblock for ultravioletprotection. While sunblock affordsno protection against the jellyfishlarvae, it does not increase the riskof trapping the larvae against theskin, as T-shirts do. Bathers shouldshower as soon as possible afterswimming, without their bathingsuits, which should be washed indetergent and heat-dried.