Jellyfish live in all of the world's oceans. Their trailing tentacles contain stinging units called nematocysts that can inject poison through human skin, causing burning pain, tingling or numbness, itching, and blisters. In more serious cases, systemic symptoms like vomiting, weakness and muscle spasms occur. Most jellyfish stings do not require medical treatment, but in rare cases of widespread stings or a sting from a highly poisonous species, the venom can be fatal.
Seawater
Immediately after a sting, gently pouring saltwater over the site can remove any remaining pieces of tentacles. The Mayo Clinic warns against using freshwater because it can activate more of the stingers.
Vinegar
Pouring vinegar over the site of the sting will deactivate the stingers for some types of jellyfish but can activate the stingers of other species. Do not use vinegar in cases of stings from Chesapeake Bay sea nettles, which are brown or red and found in large groups, or Portugese-Man-of-War jellyfish, which have a distinctive purple bubble-like top and are common off the East and West coasts of the United States.
Paste
To remove any remaining stingers, which are too small to see with the naked eye, make a paste of saltwater and baking soda or talcum powder. Baking soda paste has the added benefit of relieving the pain. Apply the paste to the site of the sting, and when it hardens and dries, scrape it off with a credit card or similar object---do not use an unprotected finger, because it can be stung.
Pain Relief
Soaking the area of the sting in hot water---as hot as the patient can tolerate---for about 20 minutes can soothe the skin, but be sure that all of the stingers are removed before trying this. After a soak, applying ice packs or corticosteroid skin creams and taking an over-the-counter pain reliever, such as aspirin or ibuprofen, can also relieve the pain of a jellyfish sting.
Medical Treatment
Systemic symptoms that occur, such as a change in breathing or disorientation, require emergency medical attention, states the Merck Manual. In severe cases, a doctor might administer an epinephrine injection and intravenous fluids to prevent or reverse shock. Intravenous pain medication can control cases of severe pain and benzodiazepines can halt muscle spasms. In cases of stings from a species of box jellyfish or sea wasp found in the Indo-Pacific ocean, doctors will administer an antivenom. Although tiny, these jellyfish pack a powerful venom that is life-threatening.
