Local Allergic Reactions

Two or three days after diving, I get skin eruptions that are slightly painful, itchy and filled with liquid. I usually get about 10 eruptions on my face, hands, forearms and shins. This condition occurs both with and without a full wetsuit. My husband, who dives with me, is not affected by this problem. Is my condition related to swimmer's itch? Is there any way to prevent it from occurring? How should I treat it once it does occur?

The most likely causative agent is a biting insect or marine creature capable of stinging a human.

Seabather's Eruption

Could this be the result of an attack by sea lice, termed ‘seabather's eruption’ – a cluster of stings from small thimble jellyfish or larval forms of sea anemones? Perhaps, although one would expect a more intense skin reaction around your neck and wrists, along and under bathing suit lines, and representative of an assault by thousands of stinging cells simultaneously. Given the pattern, probably not.

Anemone Sting

The intense redness and blisters are reminiscent of stings by sea anemones, particularly those which burrow in the sand, although you would most likely recollect having handled such creatures. Similarly, fire coral is unlikely if there is no mention of your contact with their clearly visible calcareous pillars. Hydroids are often widespread and fragile, and can leave stinging fragments invisible in the water, so a hydroid sting is a distinct possibility.
 
Photosensitive Reaction

It's difficult to make a precise diagnosis, because there is no ‘smoking gun’. Of course, we shouldn't overlook a drug eruption (rash) related to a possible interaction between a medication and exposure to the sun (ultraviolet radiation). This can cause a rash similar to yours. Additional questions to answer include whether you take any medications regularly, and if you were wearing a protective sunscreen at the time of your injury.

Treatment and Prevention

After the blisters occur, treat the rash as you would a second-degree (blistering) burn, by keeping the affected area clean, applying a thin application of non-sensitizing topical antiseptic ointment such as mupirocin (Bactroban), and observing for the onset of infection. If the rash becomes incapacitating because of pain or itching, you might want to ask a physician to examine you and determine whether a hypersensitivity (allergic) reaction exists. If so, the physician would most likely treat you with a glucocorticoid (steroid) drug. You could take this type of medication by mouth or by injection - I would not expect a topical steroid cream or ointment to be of any particular benefit, and would not recommend its use, because of the effect of decreased wound healing and possible increase in the chance for infection.

In terms of prevention, I would advise you to wear sunscreen and insect repellent, particularly the latter if insect bites are a possibility. There is a commercially available topical sunscreen/jellyfish sting inhibitor product (Safe Sea: www.nidaria.com) designed to protect against marine stings, which is currently being tested against many jellyfish species. I would also advise full wetsuit or diveskin protection while in the water. If you use your hands a lot while diving, you should wear dive gloves.