Hi devjr,
While I of course cannot be certain, I rather suspect that this is what you may be referring to. The below is an edited version from my "Ask RSD" column of the October 1999 issue of "Rodale's Scuba Diving" magazine:
"I. What are "sea lice" and what can I do about them?
A common form of skin disorder after diving is Sea Bather's Eruption, or SBE. Often mistakenly attributed to "sea lice," which are parasites of fish, SBE is primarily caused by the larval form of thimble jellyfish, very small creatures which float near the surface. Found in Florida, Mexico and the wider Caribbean, they are most numerous from March to August, with early April to early June being peak season.
The main feature of SBE is raised and itchy red welts/blotches which appear 4 to 24 hours after swimming or diving. The larvae tend to attach to swim wear, dive suits and hair, causing the skin under covered areas of the body and around the back of the neck to be most affected. Depending on exposure and individual sensitivity, there may be fever, headache, nausea, vomiting, generalized weakness or chills.
Prevention of stings is the best way to combat SBE. You should: (1) Ask resorts and dive shops if they are aware of heavy infestation; (2) Wear a snug fitting full body protective suit which fits tightly at the neck, wrist and ankle. Swim suits and T-shirts are not recommended; (3) Apply a thin layer of sun protectant, baby oil or petroleum jelly to the skin; (4) Remove wet garments immediately and wash yourself thoroughly. Do not rinse off with any items on; and (5) When surfacing, vigorously purge your second stage above your head just before breaking the water. If on a night dive, turn your light off at the safety stop and keep it off.
If you do get stung: (1) Immediately apply a mixture of 1/2 isopropyl alcohol and 1/2 vinegar to affected skin areas, or whatever is on the boat for such stings. Allow it to dry. Or, put on a thin paste of meat tenderizer and allow to dry. In place of meat tenderizer, some find it more soothing to rub the area with papaya if it is readily available. (2) Bathing in or applying colloidal oatmeal, which can be purchased at the pharmacy or grocery store, may afford additional relief. Follow these actions with the topical application of hydrocortisone cream/lotion, twice a day. If you do not have or cannot use hydrocortisone, Calamine lotion with menthol can be applied; (3) Given that there are no contraindications, take an oral antihistamine (nonsedating type if you are going to continue diving) if the allergic reaction continues; and (4) Wash all garments well in warm, soapy water and let dry completely before wearing again.
Remember that if you have a severe allergic reaction, or don't get substantial resolution from self treatment, or the eruption seems to be getting worse or infected, you should seek medical attention in a timely manner."
Best regards.
DocVikingo
