Welcome to the Caribbean Sea Lice Season

Every year more than one Undercurrent reader writes us about painful days on Little Cayman or misery in the Florida Keys. The problem -- called Sea Bather’s Eruption -- is a nasty rash under their wetsuit or skins, leading to an itch so severe it’s almost enough to drive them crazy. The season? March to August.

For decades, an old wives’ tale warned Bahamians against ocean swimming between Mother’s Day and Father’s Day because of the nasties. Yet it wasn’t until 1992 that marine biologists at the University of Miami determined that the cause was not “sea lice” but stinging cells called nematocysts, most of which come from the larva of thimble jellyfish.

According to Boca Raton Community hospital researchers Mary T. Russell, R.N., and Robert S. Tomchik, M.D., the organism, which looks like a speck of finely-ground pepper, floats near the surface and gets “netted” by wetsuits, skins, and bathing suits. Friction between the apparel and the skin caused by pulling off a wetsuit, simply sitting down, or even rinsing with fresh water with your suit still on can trigger the nematocysts to fire.

It may take up to twenty-four hours to feel the first prickling sensation, which can be followed by intense itching, nausea, vomiting, diarrhea, headache, muscle spasms, a sense of malaise, and trouble sleeping.

To treat, apply an antihistamine, such diphenhydramine hydrochloride, followed by 0.5% hydrocortisone cream. DAN suggests beginning with a rinse of vinegar or rubbing alcohol and notes that calamine lotion may be soothing.

Unfortunately, the only way you’ll know that the larva are present is by observing an eruption in one of your fellow divers. To make sure that first-erupting diver isn’t you, Russell and Tomchik recommend you slip out of your dive apparel as soon as possible, then shower off loose larvae. If you must wear your suit again, try to wash it out with detergent and heat dry it. Air-dried nematocysts still have the ability to fire.