What You Need to Know about Lion’s Mane Jellyfish

A lion's mane jellyfish swimming in the water.

From Quincy down to Cape Cod, we’re lucky to have several wonderful beaches across the South Shore. 

With summer in full swing, plenty of South Shore residents are heading to those beaches to seek relief from the heat — at the appropriate social distance, of course.

While we’re all accustomed to taking precautions at the beach to protect from things like sunburns or greenhead flies, there’s a new issue has arisen over the past couple of weeks: lion’s mane jellyfish.

These jellyfish have been spotted at several South Shore beaches, including beaches in Quincy, Weymouth, Hingham, Marshfield, and Duxbury. 

There have been numerous sightings in towns on the North Shore and elsewhere in New England as well.

Are lion’s mane jellyfish dangerous?

Like many jellyfish, lion’s mane jellyfish have long tentacles that they use for protection and to obtain food. These tentacles can sting, and that sting is painful to humans.

While the sting of a lion’s mane jellyfish isn’t poisonous, it can cause severe allergic reactions in some people.

What should I do if I see a lion’s mane jellyfish?

Because of their painful sting, the safest thing to do is to avoid these jellyfish. If you see lion’s mane jellyfish in the water, it’s best to exit the water until they pass by.

If there’s a lion’s mane jellyfish on the sand, avoid the area and do not attempt to move it, as some jellyfish can still sting out of the water.

How should a jellyfish sting be treated?

If you or a family member get stung by a lion’s mane jellyfish, don’t panic: as stated above, these stings may be painful, but they are rarely fatal.

  • Exit the water and inspect the area of the sting. If any tentacles remain on the skin, do not touch them with your hands; instead, use tweezers to remove any remnants.
  • If you’re at a public beach, alert the nearest lifeguard. Lifeguards often have jellyfish sting kits on hand, and are usually trained in how to treat stings.
  • Flush the affected area with hot water — if you have access to a shower or tub, soaking the skin in hot water is even better.
  • To manage any pain you’re experiencing, you can take ibuprofen or acetaminophen. If there’s any swelling, an antihistamine like diphenhydramine can help. 


How can I tell if a sting has caused an allergic reaction?

Allergic reactions to jellyfish stings cause symptoms similar to those of other allergies, namely trouble breathing, fever, nausea, dizziness, fainting, and headache.

When should I seek medical attention for a jellyfish sting?

In the majority of cases, lion’s mane jellyfish stings will only cause mild symptoms. 

However, if you experience any symptoms consistent with an allergic reaction to the sting, it’s important to seek medical attention immediately.

If you don’t have symptoms of an allergic reaction but are still experiencing lingering pain, swelling, or redness several days after the sting, consider visiting an Urgent Care center to confirm that there is nothing else going on.

Jellyfish stings are one of many things we're able to treat at one of our Health Express locations.

Learn more about Health Express.