You look forward to your family vacation all year: the sun, sand, surf. But who invited the jellyfish?

Frolicking in the ocean is a summertime rite of passage, but a jellyfish sting can spoil the fun. Here's how to handle it if someone in your family gets zapped by one of these mysterious sea creatures.

About Jellyfish

Jellyfish have been around for millions of years (they predate dinosaurs) and live in oceans all over the world. You might have noticed on visits to the beach that many days there are none to be seen; other times, you might spot a bunch of them among the waves or washed up on the beach.

There are many different types of jellyfish, and while their appearances can vary greatly, they all have the gelatin-like composition that gives them their name. Some just look like small, clear blobs, while others are bigger and more colorful with tentacles hanging beneath them.

It's the tentacles that cause the stings. To eat, jellyfish sting their prey with their tentacles, which release a venom that paralyzes their targets. Jellyfish don't go after humans, but someone who swims up against or touches one — or even steps on a dead one — can be stung all the same.

While jellyfish stings are painful, most are not emergencies. Expect pain, red marks, itching, numbness, or tingling with a typical sting.

But stings from some types of jellyfish — such as the box jellyfish (also called sea wasp) — are very dangerous, and can even be deadly. These jellyfish are most often found in Australia, the Philippines, the Indian Ocean, and central Pacific Ocean.

When Jellyfish Sting

Jellyfish stings leave thousands of very tiny stingers called nematocysts in the skin. These stingers can continue to release jellyfish venom (poison) into the body. Sometimes, they can be rinsed off with seawater or scraped off.

One old folk remedy touts peeing on a jellyfish sting. But experts recommend rinsing with seawater and vinegar instead. Vinegar is a weak acid that, for many kinds of jellyfish stings, might keep the nematocysts from "firing," or releasing venom. Similarly, seawater from the jellyfish's home environment also seems to prevent them from firing. Fresh water, though, may cause the stingers to fire.

If your child is stung:

• Remove him or her from the water.
• Rinse the area with seawater. (Fresh water can prompt the stingers to release more venom.)
• Don't rub the area, which can make things worse.
• With many types of jellyfish stings, it helps to soak the area of skin with vinegar for 15 to 30 minutes.
• Use a credit card to scrape off the stingers still in the skin. If available, put shaving cream or a paste of seawater and baking soda on the area. Then scrape it off.
• Check in with your doctor to see if pain relievers might help your child feel better.

Call an ambulance immediately if someone has been stung and:

• is having trouble breathing or swallowing
• has a swollen tongue or lips, or a change in voice
• has bad pain or feels generally unwell
• has stings over a large part of the body
• the sting is in the eye or mouth

Avoiding Jellyfish Stings

Reduce your family's chances of a jellyfish encounter by swimming only at guarded beaches, which are more likely to warn visitors about jellyfish. Look for a sign or warning flag (some beaches fly a purple warning flag when there's "dangerous marine life" in the water). Also consider stashing a small container of vinegar in your beach gear, just in case.

Reviewed by: Larissa Hirsch, MD
Date reviewed: August 2011