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Sea Bathers Eruption (aka: sea lice, ocean itch)

I was snorkeling in the ocean outside my hotel in the Florida Keys. Soon after exiting the water, my skin started to tingle. I quickly showered in an attempt to remove the offending agent and noted that the stinging sensation intensified. A bumpy, itchy rash erupted within the hour and I’m miserable. What is this and what should I do?

Last updated 28, March 2013
Sea Bather's Eruption
Seabather’s eruption, often misnamed "sea lice" (which are true crustacean parasites of fish), refers to dermatitis (skin irritation) that results from contact with ocean water containing various larval species of jellyfish and anemones. The incidence of larval blooms appears higher in warmer oceans and affects people all over the world. Most noted species in the Western hemisphere are the thimble jellyfish, Linuche unguiculata and sea anemone Edwardsiella lineate (seen in August – November as far north as Long Island, New York)1,2,3. Seasonal peaks of thimble jellyfish occur in the Caribbean and southern Florida during May, but are present throughout the summer (April – August)1,4,5,6,7. Seabather's eruption predominately affects areas covered by clothing: bathing suits, swim caps, shirts, rash guards and wetsuits1. Those swimming at the surface may suffer stings to the exposed neck and scalp1. In areas with heavy boat traffic, jellyfish may become fragmented, which can facilitate stings to any exposed area1.
Stings are characterized as a tingling sensation that may begin while still in the water or soon after exiting. While tempting to bathe, the application of freshwater may intensify the sting1.The ensuing rash usually consists of extremely itchy red bumps, wheals, blisters and papules, which may become dense and confluent (run together in a mass). Skin eruptions may present within minutes or up to 12 hours after exiting the water and can persist for 4-weeks (in severe cases)1. Severe exposure can result in systemic symptoms such as fevers, chills, headache, fatigue, nausea, conjunctivitis (itchy red eyes) and urethritis (burning on urination)1. Susceptibility and presentation will vary by individual. Children, and those previously sensitized may have more severe skin reactions.
As with stings from other Cnidarians (jellyfish, fire coral and anemones), treatment consists of immediate application of vinegar, removal of any remaining marine organisms, and the use of topical steroids (which reduce itch and inflammation). In severe cases, systemic corticosteroids and antihistamines may be helpful1. Signs of infection or severe systemic symptoms should prompt medical attention.
The stinging cells may remain in bathing suits or clothing, even after drying. To prevent subsequent inoculation, machine wash or thoroughly rinse in vinegar.
Authors: Nicholas Bird MD, MMM
Matias Nochetto, MD
1.Auerbach, Paul. Envenomation by Aquatic Invertebrates (Ch 80). Wilderness Medicine, 6th Ed. 2012. PP 1596-1628.
2.Freudenthal AR: Seabather's eruption: Range extended northward and a causative organism identified. Rev Int Oceanogr Med 1991; 101-104:137.
3.Freudenthal AR, Joseph PR: Seabather's eruption. N Engl J Med 1993; 329:542.
4.Haddad V, Cardoso JL, da Silveira FL: Seabather's eruption: Report of five cases in southeast region of Brazil. Rev Inst Med Trop S Paulo 2001; 43:171.
5.Jefferies NJ, Rushby N: Caribbean itch: Eight cases and one who didn't (Exercise Blue Calypso Diamond). J R Army Med Corps 1997; 143:163.
6.Tomchik RS, Russell MT, Szmant AM, et al: Clinical perspectives on seabather's eruption, also known as “sea lice.”. JAMA 1993; 269:1669.
7.Vallely A, Vallely L: Seabather's eruption in Papua New Guinea. Trop Doct 1998; 28:53.