Seabather's eruption is an itching dermatitis caused by a hypersensitivity reaction to the immature nematocysts of larval-stage thimble jellyfish (Linuche unguiculata), sea anemones (Edwardsiella lineata) and other larval cnidarians. The term "sea lice" is also sometimes used to describe seabather's eruption, although it is not in fact caused by the sea louse, a parasite that affects only fish.
Symptoms generally arise later after one takes a shower. It is unusual to notice the eruptions immediately. Symptoms can last from a few days up to two weeks, the shorter time being the norm.
The reaction is identified by severe itching around small red papules 1mm to 1.5 cm in size located on areas of skin that were covered by water-permeable clothing or hair during ocean swimming. Initial swimmer exposure to the free-floating larvae produces no effects, as each organism possesses only a single undeveloped nematocyst which is inactive while suspended in sea water. However, due to their microscopic size and sticky bodies, large concentrations of larvae can become trapped in minute gaps between skin and clothing or hair. Once the swimmer leaves the ocean, the organisms stuck against the skin die and automatically discharge their nematocysts when crushed, dried out, or exposed to fresh water. This is why symptoms usually do not appear until the swimmer dries themselves in the sun or takes a freshwater shower without first removing the affected clothing.
At certain times of the year this can be a problem in some areas of the Bahamas particularly around New Providence.
Cases have been found in Bermuda in 2011, 2014 and 2015 with Paradise Lakes proving particularly bad. In 2015 many felt the effects after swimming in Mangrove Bay and Harrington Sound.
Seabather's eruption is also an issue in various parts in Anilao and Mindoro in the Philippines. This typically occurs within 30 ft. below surface, just above the coral reefs. Snorkelers are most prone because of their proximity to the surface. Scuba divers encounter less of this, and usually in shore dives. The occurrence of stinging is highly probable whenever plankton is abundant.
Occurrences in Thailand indicate that the eruption isn't an isolated issue for Florida. As recently as October 2007, individual reports indicate that cnidarian larvae capable of causing Seabather's eruption are present in the Gulf of Siam along the western coast area near Hua Hin. In January 2014, reports of larvae and Seabather's eruption occurred around Koh Phi Phi and Ko Yao Noi. An outbreak in Koh Phi Phi occurred in March, 2016.
Cases were first identified in Brazil in 2001.
Cases of seabather's eruption occur in Hawaii and many of the states along the Gulf of Mexico during the summer months. Cases are common from May - July in Florida, and in certain parts of Hawaii from April - August. South facing Hawaii beaches are most impacted by jellyfish eight days after a full moon.
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- Hawaii: Jellyfish sting warning