Jellyfish

• Treatment
The three goals of first aid for uncomplicated jellyfish stings are to prevent injury to rescuers, deactivate the nematocysts, and remove tentacles attached to the patient. Rescuers need to wear barrier clothing, such as pantyhose, wet suits or full-body sting-proof suits. Deactivating the nematocysts (stinging cells) prevents further injection of venom.
Vinegar (3 to 10% aqueous acetic acid) is a common remedy to help with box jellyfish stings, but not the stings of the Portuguese Man o' War (which is not a true jellyfish, but a colony). For stings on or around the eyes, a towel dampened with vinegar is used to dab around the eyes, with care taken to avoid the eyeballs. Salt water is also used if vinegar is unavailable. Fresh water is not used if the sting occurs in salt water, as changes in tonicity can release additional venom. Rubbing wounds, or using alcohol, spirits, ammonia, or urine may have strongly negative effects as these can also encourage the release of venom.
Clearing the area of jelly, tentacles, and wetness further reduces nematocyst firing. Scraping the affected skin with a knife edge, safety razor, or credit card can remove remaining nematocysts.