Despite their harmless-sounding name, bluebottles are sea creatures that you should steer clear of in the water or on the beach.

The bluebottle (Physalia utriculus) is also known as a Pacific man o’ war — similar to a Portuguese man o’ war, which is found in the Atlantic Ocean.

The dangerous part of a bluebottle is the tentacle, which can sting its prey and creatures they sense as threats, including people. The venom from bluebottle stings can inflict pain and swelling.

Treatments for a bluebottle sting range from a hot water soak to topical creams and ointments to traditional oral pain medications. Some home remedy solutions, such as urine, aren’t recommended, despite being widely believed as effective treatments. Here’s what you can do.

If you’re unfortunate enough to be stung by a bluebottle, try to stay calm. If possible, ask someone to stay with you and to help treat the injury.

Find a place to sit

If you’re stung in the foot or leg, walking may cause the venom to spread and expand the painful area. Try to stay still once you reach a place where you can clean and treat the injury.

Don’t itch or rub

Even though it may start to itch, don’t rub or scratch the site of the sting.

Rinse, rinse, rinse

Instead of rubbing, wash and rinse the area carefully with water.

Hot water dunk

Research shows that immersing the wound in hot water — as hot as you can stand for 20 minutes — is a proven treatment to ease the pain of bluebottle stings.

Be careful not to make the injury worse by using water that’s too hot. Ideally, water that’s about 107°F (42°C) should be tolerable to the skin and effective at treating the sting. The heat helps kill the protein in the venom that causes pain.

Ice pack

If no hot water is available, a cold pack or cold water may help ease the pain.

Take a pain reliever

An oral pain reliever and anti-inflammatory, such as ibuprofen (Advil) or naproxen (Aleve), may provide additional comfort.

First-aid boost

Boost your beach first-aid kit with these tips:

  • Vinegar. Research suggests that using vinegar as a rinse can disinfect the site of the sting and provide pain relief.
  • Tweezers. While rinsing should help remove any invisible stinging cells, you should also look for any tentacle fragments and carefully remove them with tweezers.
  • Gloves. If possible, wear gloves to avoid any further contact with your skin.
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If you still experience pain, itchiness, and swelling after the treatment outlined above, you should see a doctor. They may prescribe cortisone cream or an ointment to help reduce inflammation and ease your symptoms.

You should definitely see a doctor if:

  • the area of the sting covers a wide area, such as most of the leg or arm
  • you’re stung in the eye, mouth, or other sensitive area — in these cases, seek immediate medical assistance
  • you’re unsure if or what you were stung by

If you’re unsure whether you’ve been stung by a bluebottle, jellyfish, or other sea creature, you should see a doctor for an evaluation. Some jellyfish stings can be fatal if left untreated.

Though rare, allergic reactions to bluebottle stings can occur. The symptoms are like those of anaphylaxis, a severe allergic reaction that can follow the sting of a wasp or scorpion. If you’re stung and experience chest tightness or difficulty breathing, get medical attention immediately.

If stung by a bluebottle, you may experience the following symptoms:

  • Pain. A bluebottle sting typically causes pain right away. The pain is usually quite severe.
  • Red line. A red line is often visible, a sign of where the tentacle touched the skin. The line, which may look like a string of beads, will usually swell and become itchy.
  • Blisters. Sometimes, blisters form where the tentacle came in contact with skin.

Other symptoms, such as nausea or abdominal pain, are unlikely.

The size of the wound and the severity of symptoms depend on how much contact the tentacle had with the skin.

How long will the pain last?

The pain of a bluebottle sting can last up to an hour, though multiple stings or injuries in sensitive parts of the body can make the pain last longer.

Bluebottles feed on small mollusks and larval fish, using their tentacles to pull their prey into their digestive polyps.

Stinging tentacles are also used defensively against predators, and innocent swimmers and beachgoers can seem like a threat to these unusual creatures. Multiple stings are possible at one time, though a single sting is most common.

Bluebottles can sting in the water and on the beach when they appear to be lifeless. Because of their blue color, they’re harder to see in the water, which is one reason why they have few predators.

Though bluebottles resemble jellyfish, they’re actually a collection of four distinct colonies of polyps — known as zooids — each with its own responsibility for the creature’s survival.

What this means for people is that stinging happens on contact with the tentacle, almost like a reflex.

Your best strategy to avoid a bluebottle sting is to give them a wide berth if you spot them on the beach. And if there are warnings about dangerous animals in the water, such as bluebottles and jellyfish, heed caution and stay out of the water.

Children and older adults, as well as people who are allergic to bluebottle stings, should exercise greater caution and be accompanied by healthy adults in areas inhabited by bluebottles.

In the summer months, bluebottles are usually found in the waters around eastern Australia, while in the autumn and winter months, they can be found in the waters off southwestern Australia. They can also be found throughout the Indian and Pacific oceans.

A bluebottle’s main body, also known as a float, is usually no more than a few inches long. The tentacle, however, can be up to 30 feet long.

Because of their small size, bluebottles can be washed ashore easily by strong tidal action. They’re most commonly found on beaches after powerful onshore winds. Bluebottles are less commonly seen in sheltered waters or on the banks of sheltered coves and inlets.

Because their blue, translucent bodies make them difficult to spot in the water, bluebottles sting tens of thousands of people in Australia every year.

Though painful, the stings aren’t fatal and don’t usually cause any serious complications. Still, it’s worth paying close attention when you’re in the water or on the beach to avoid these unusual but dangerous creatures.

If a bluebottle tentacle does find you, be sure to carefully clean the sting and soak it in hot water to start the healing process.