Treating Jellyfish Stings and Man-o-War Stings

Jellyball Jellyfish
Nonvenomous Jellyfish, or Jellyball. Getty Images

It's beach weather! The ocean is full of fun, but it's also full of wildlife, including jellyfish. Do you know what to do if you or someone with you sees a jellyfish or is stung by one? You should know the answer to these questions before you go to the beach since an encounter with a jellyfish can be a painful or possibly lethal experience. As a matter of practical chemistry, your biggest risk from a jellyfish or man of war sting may come from improper first aid intended to deal with the venom, so pay attention...

Key Takeaways: Treating Jellyfish and Man of War Stings

  • Jellyfish and the Portuguese man-of-war can deliver painful and potentially life-threatening stings.
  • The first step of first aid is to remove the victim from the water. While some people are allergic to venom, the main risk comes from drowning.
  • Seek emergency aid if the victim is having trouble breathing.
  • For simple stings, use a shell or credit card to remove any tentacles clinging to skin.
  • Vinegar is the most common chemical used to deactivate the stinging cells. While it's fine to use salt water to rinse the area, fresh water should be avoided because it can cause stinging cells to release venom all at once.
  • It's best to avoid jellyfish. Tentacles from dead animals can still sting!

Question: What should you do if you see a jellyfish?
Best Answer: Leave it alone.
If it's in the water, get away from it. If it's on the beach and you need to walk around it, walk above it (dune side) rather than below it (surf side), since it may be trailing tentacles. Keep in mind a jellyfish does not need to be alive in order to sting you. Detached tentacles are capable of stinging and releasing venom for several weeks.
My Actual Answer: It depends on what kind of jellyfish it is.
I realize if it looks like floating jelly, it's considered a "jellyfish," but there are different types of jellyfish and also animals that look like jellyfish but are something else entirely. Not all jellyfish can hurt you. The jellyball pictured above, for example, is common off the coast of South Carolina, where I live. What do you do when you see one? If you are a kid, you'll probably pick it up and throw it at another kid (unless it's alive and then you avoid it because they kind of hurt when the waves throw one at you). This is a non-venomous jellyfish. Most parts of the world have non-venomous jellyfish, which tend to be easy-to-spot. It's the jellyfish you don't see that present the biggest threat. Many jellyfish are transparent. The moon jellyfish is a common example. You probably won't see them in the water, so if you are stung you won't know exactly what got you. If you see a jellyfish and don't know what type it is, treat it like a venomous species and get away from it.

Portuguese man of war on a beach
The Portuguese man of war has a pink or blue float. Darieus / Getty Images

Question: How do I treat a jellyfish sting?
Answer: Act quickly and calmly to remove the tentacles, stop the stinging, and deactivate any toxin.
Here is where people get confused because the best steps to take depend on what type of animal caused the sting. Here's a good basic strategy, especially if you don't know what caused the sting:

  1. Get out of the water. It's easier to deal with the sting and it takes drowning out of the equation.
  2. Rinse the affected area with sea water. Do not use fresh water! Fresh water will cause any stinging cells that haven't fired (called nematocysts) to do so and release their venom, possibly worsening the situation. Do not rub sand on the area (same reason).
  3. If you see any tentacles, carefully lift them off the skin and remove them with a stick, shell, credit card, or towel (just not your bare hand). They will stick to swimwear, so use caution touching clothing.
  4. Keep an eye on the victim. If you see any signs of an allergic reaction, call 911 immediately. Symptoms could include difficulty breathing, nausea, or dizziness. Some redness and swelling is normal, but if it spreads outward from the sting or if you see hives on other parts of the body, that could indicate an allergic response. If you suspect a reaction, do not hesitate to seek medical attention!
  5. Now... if you are sure the sting is from a jellyfish and not a Portuguese Man of War the Man of War is not a true jellyfish) or any other animal, you can use chemistry to your advantage to inactivate the toxin, which is a protein. (Technically the venom tends to be a mixture of polypeptides and proteins including catecholamines, histamine, hyaluronidase, fibrolysins, kinins, phospholipases, and assorted toxins). How do you inactivate proteins? You can change the temperature or acidity by applying heat or an acid or base, such as vinegar or baking soda or diluted ammonia, or even an enzyme, such as the papain found in papaya and meat tenderizer. However, chemicals may cause the stinging cells to fire, which is bad news for someone allergic to jellyfish toxin or anyone stung by a Portuguese Man of War. If you do not know what caused the sting or if you suspect it is from a Man of War, do not apply fresh water or any chemical. Your best course of action is to apply heat to the affected area since it penetrates the skin and inactivates the toxin without causing more venom to be injected. Also, heat quickly helps alleviate the pain of the sting. Hot seawater is great, but if you don't have that handy, use any warmed object.
  6. Some people carry aloe vera gel, Benadryl cream, or hydrocortisone cream. I'm not sure how effective the aloe is, but Benadryl is an antihistamine, which may help limit an allergic response to the sting. Hydrocortisone can help reduce inflammation. If you seek medical attention and used Benadryl or hydrocortisone, be sure to alert the medical professionals. Acetaminophen, aspirin, or ibuprofen commonly are used to relieve pain.
    The Portuguese Man of War (Physalia physalis) looks a lot like a jellyfish, but it is a different animal. While the blue or pink sail cannot harm you, the trailing tentacles pack a potentially-lethal sting. The tentacles can sting you even if the animal is dead.
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Your Citation
Helmenstine, Anne Marie, Ph.D. "Treating Jellyfish Stings and Man-o-War Stings." ThoughtCo, Apr. 5, 2023, Helmenstine, Anne Marie, Ph.D. (2023, April 5). Treating Jellyfish Stings and Man-o-War Stings. Retrieved from Helmenstine, Anne Marie, Ph.D. "Treating Jellyfish Stings and Man-o-War Stings." ThoughtCo. (accessed June 8, 2023).