Sea anemones are colorful coelenterates (related to corals, jellyfish, and Portuguese man-of-war) with stinging cells (nematocysts). Over 1000 species live within the tidal zones of tropical, subtropical, and temperate waters. They range in size from a few millimeters to more than 0.5 meters (1.7 feet).

Sea anemone stings typically occur when they are accidentally brushed up against or purposely touched by the unknowing. Initial symptoms vary from a prickly sensation to severe burning at the wound site. The pain increases in intensity and may extend proximally into local lymph node basins. After a few hours, the pain lessens, but a residual ache or itch may last for weeks.

The skin reaction varies by sea anemone species. Secondary infection may occur. Systemic symptoms may be reported and include fever, chills, malaise, nausea, vomiting, abdominal pain, headache, delirium, and muscle spasms. Shock, fulminant liver failure, renal failure, and respiratory distress have been reported.