Lyngbya dermatitis (toxic seaweed dermatitis)

Lyngbya dermatitis is an irritant contact dermatitis caused by the blue-green alga (or cyanobacterium), Lyngbya majuscula, commonly found in tropical and temperate waters worldwide. Lesions generally appear in a bathing suit distribution minutes to hours after exposure, initially with itching or burning, evolving into a blistering eruption which eventually desquamates leaving bright red, tender erosions that resolve spontaneously in about a week. Our case is of a 13-year-old female that presented with haphazard clusters of reddish-brown vesicles and papules on her abdomen one day after swimming in rough surf conditions on the shores of Oahu, Hawaii. Histopathological examination revealed an acute irritant contact dermatitis consistent with Lyngbya dermatitis. L. majuscule, with its wealth of biologically active compounds, should be a consideration in any patient presenting with an acute irritant contact dermatitis following temperate saltwater exposure.