seabather's eruption

noun

sea·​bath·​er's eruption ˈsē-ˌbā-t͟hərz- 

: acute pruritic dermatitis that occurs on parts of the body covered by a swimsuit within 24 hours after exposure to seawater containing certain tiny coelenterate larvae (as of jellyfishes, sea anemones, or corals) and that is caused by nematocysts fired by the larvae caught in the mesh of the bathing suit or compressed between the bathing suit and the skin see thimble jellyfish