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clock-iconPUBLISHEDDecember 5, 2025

Seal Finger: What Is This Horrible Infection That Makes Your Hand Swell Like A Balloon?

Don't do this if you like having functional hands.

Rachael Funnell headshot

Rachael Funnell

Rachael has a degree in Zoology from the University of Southampton, and specializes in animal behavior, evolution, palaeontology, and the environment.

Senior Science Writer

Rachael has a degree in Zoology from the University of Southampton, and specializes in animal behavior, evolution, palaeontology, and the environment.View full profile

Rachael has a degree in Zoology from the University of Southampton, and specializes in animal behavior, evolution, palaeontology, and the environment.

View full profile
EditedbyLaura Simmons
Laura Simmons headshot

Laura Simmons

Health & Medicine Editor

Laura holds a Master's in Experimental Neuroscience and a Bachelor's in Biology from Imperial College London. Her areas of expertise include health, medicine, psychology, and neuroscience.

person touches a seals head, risky business if you don't want seal finger

Yes, we know they’re friend-shaped, but the bacteria in their mouths? Less so.

Image credit: Zsolt Biczo / Shutterstock.com


Evolution really popped off the day it made a seal. The playfulness of a dog with the attitude of a fat happy cat who occasionally gets dolphinesque zoomies. What’s not to love? Seal finger, that’s what.

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Yes, approach these friend-shaped foes on the beach and you risk getting a serious bacterial infection that sailors have feared for hundreds of years. Known as seal finger because of its prevalence among those working with seals or seal meat, we didn’t unmask its true identity until 1991.

What is seal finger?

Seal finger is a kind of infection that develops after a person is either bitten by a seal, or handles seal products when they have a cut on their hands. Historically it’s been common among sailors, fishers, divers, biologists, and vets, and it used to be an illness that came with serious consequences.

What are the symptoms of seal finger?

The leading symptom of seal finger is pain. In fact, the pain could be so severe that sailors would request the affected finger be cut off so that they could carry on working and not lose wages.

That pain is accompanied by swelling that can extend to the entire hand, blowing it up like a latex glove. The infection can attack the joint, too, and without prompt treatment stiffness and loss of function can be permanent.

What causes seal finger?

Seal finger is thought to be the clinical manifestation of infection with a bacterium called Mycoplasma phocacerebrale. It was identified as the primary cause in 1991 after it was detected both in a painful bite on a human hand and inside the mouth of the seal that bit it.

It’s a normal part of the microbiome found in a seal’s mouth and nose, but in a human hand it can cause chaos. The good news? It can be treated with antibiotics, but prompt diagnosis and the correct course of treatment is crucial to making a good recovery from seal finger.

So, if you see a plump seal pup on the beach, just remember: keep your hands to yourself. Oh, and if seal finger isn’t enough to put you off, might we draw your attention to the fact that seals have nails – just take a look at this cursed pinnipedicure.


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