Dr. Jeff Hersh: Treat sea urchin stings by removing spine, add warm water, vinegar

Dr. Jeff Hersh
·4 min read

Q: During my last day of vacation, I got a painful sting from a sea urchin while snorkeling. Should I be worried?

A: Sea urchins (a type of echinoderm, in the same general family as starfish and sea cucumbers) are spherical or flat animals completely covered with spines (spike-like protrusions) that act as their form of defense. They are found pretty much all over the world.

Unlike some spiney land animals (for example, porcupines or hedgehogs), or even some spiney sea animals (such as lionfish), they are not very mobile. Therefore, sea urchins do not attack; instead, their long, hard spines (which are made of calcium carbonate) are more of a passive defense and require something to be bumped/pushed into them (not dissimilar to the defense of certain plants, such as the spines on some cacti or the thorns on roses or other plants) in order for them to react.

Dr. Jeff Hersh
Dr. Jeff Hersh

So a human sting by a sea urchin typically occurs when someone steps on it (the most common way) or swims/is pushed (by the current, their own errant swimming or something else) into one.

The sea urchins’ spines protect them in two ways:

  • The mechanical protection of their spines potentially stabbing whatever comes in contact with them;

  • A toxin on these spines that increases the pain from the sting and which may cause other symptoms/complications. The tips of a few of the almost 1,000 species of sea urchins’ spines, for example the flower urchin, also have tiny "claw-like" pincers (called pedicellariae) that enable them to inject an even more toxic venom.

Being stuck by a sea urchin’s spiney stinger is typically immediately painful (which can be intense, due to the toxin, but is usually much improved within a day or so and usually resolved by four or five days) and may include redness, swelling and/or bleeding at the puncture wound site. If the sting is superficial, it behaves similarly to many other superficial puncture injuries (such as a finger prick from a rose thorn) and resolves on its own, although there is still some risk it could become infected.

If the puncture wound is deeper, and especially if there are retained fragments of the spine that have broken off into the wound, the risk of infection is greatly increased, and the retained fragment can also cause irritation and may even migrate within the victim to cause complications (such as pushing on a nerve). In some cases, the infection could become systemic and cause fever and/or other complications, possibly (but rarely) including sepsis and even death.

A sting from one of the species of sea urchins with more toxic venom can cause more severe systemic symptoms such as weakness, nausea, vomiting, muscle aches, muscle paralysis, breathing issues and even death.

The diagnosis of a sea urchin sting is made by the history (including contact with a sea urchin or at least a risk of it having happened) and symptoms/physical findings noted above. Although X-rays (or other imaging) may help identify a retained spine fragment, they may also not be able to visualize it, so a high index of suspicion is needed.

There is no antivenom for a sea-urchin sting, so treatment includes:

  • Immediate removal of the spine (similar in concept to removing a splinter to prevent complications). Try to ensure the removal process does not cause part of the spine to break off and be retained.

  • Ensuring the patient’s tetanus shot is up to date.

  • Soaking the area in very warm water (salt water or saline is usually recommended, if possible), being sure not to burn the patient; this may help the pain and reduce symptoms because the toxins from sea urchin spines are heat labile.

  • Treating the wound with vinegar to help dissolve any remaining spine (as I noted in a prior column for jelly fish stings, urine is not helpful; that is an old wives’ tale erroneously promulgated in movies and TV shows).

  • Giving other supportive care as clinically indicated.

  • Surgery in certain uncommon cases to remove retained spine fragments.

As always, an ounce of prevention is worth a pound of cure, so people should avoid sea urchin contact. This should start by staying away from the coral (also so as not to damage it) and not disturbing these beautiful sea creatures.  Being extra careful where you step and what you bump into, as well as wearing flippers/shoes and protective gear (such as a wet suit, etc.) to protect yourself in case you accidentally do contact a sea urchin, are also indicated.

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.

This article originally appeared on MetroWest Daily News: Dr. Jeff Hersh explains how to respond to sea urchin sting