What is sea-bathers eruption?

Sea-bather's eruption is an itching dermatitis that typically appears on covered areas of the skin (under bathing suits, shirts, long hair) caused by a hypersensitivity reaction to the immature nematocysts of larval-stage thimble jellyfish (Linuche unguiculata), sea anemones (Edwardsiella lineata) and other larval cnidarians.  Initial swimmer exposure to the free-floating larvae produces no effects, as each organism possesses only a single undeveloped nematocyst (stinging cell) which is inactive while suspended in seawater.  Once the swimmer leaves the seawater, the organisms stuck against the skin die and automatically discharge their nematocysts when crushed, dried out, or exposed to freshwater causing the irritation.

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