If you are swimming in the ocean, there is a chance that you get stung by a jellyfish. Be careful while swimming, keep your eyes out for jellyfish, and follow these steps should you be stung.
Get out of the water and to a safe spot. If you have been stung, you will know it right away by the sharp pain that comes with it. Get out of the water as quickly as possible; the venom from the jellyfish could make it difficult for you to swim.
If you need help, make a lot of noise to get attention. Call 911 if you are showing signs of allergic reaction such as wheezing, difficulty breathing, swelling of the face or throat, upset stomach, or vomiting.
Hold still and apply vinegar. It is important that you hold as still as possible while treating a jellyfish sting. This is because the venom of the sting will spread as you move. You should then deactivate the stinging cells with vinegar. If you don't have vinegar, use the saltwater from the ocean. Do not urinate on it! It is also important that you don't put fresh water on it because this could cause the release of more venom.
You can then remove the remaining tentacles with tweezers, a glove, or another object. Make sure you don't touch them or they will sting you.
If possible, lather the area with shaving cream and shave it with a safety razor. The purpose is to "shave" off any remaining tentacles. If no shaving supplies are available gently cover with moist sand and use a shell or credit card.
Rinse off with additional vinegar. This will rinse away any sand or shaving cream that remains without causing any remaining cells to add additional venom to the wound.
Treat pain with baking soda and water, ice, antihistamines, and/or oral pain relievers. Pain should be dissipating over time. You can apply an ice pack wrapped in a towel to the area for some relief. Don't leave it there more than ten to fifteen minutes, and don't let melting water touch the wound.
You can also make a paste of baking soda and water, and see if that helps with the pain. Leave the mixture on there for fifteen to twenty minutes.
Cortisone and other antihistamines can also help (both topical and oral). You can also take oral pain relievers for help in the pain.
Seek medical attention if allergic symptoms occur or pain does not diminish. If you are still having problems with the sting after 48 hours, then you should seek the help of a doctor. You should also seek a doctor if, at any time, you are starting to see signs of an allergic reaction.
Most jellyfish stings are painful, but not serious. You won't need a doctor's attention for most of them. It should be noted, however, that these treat jellyfish stings. Portuguese Men-of-War (blue bag like creatures that float on top of the water) aren't real jellyfish and should not be treated with mere vinegar; different steps must be taken if you were stung by a Man-of-War (you should be able to see a Man-of-War as you are retreating from the source of the sting). You can also seek help from a lifeguard, who should know what to do. Many will even have tools and supplies to do it.
If you are swimming in Australia, seek the help of a lifeguard, seek medical attention, or call 911 if the pain is unbearable. There are many dangerous jellyfish in Australia, including the box jellyfish, whose stings are fatal. If at any times you have questions or concerns, call your doctor.