While spending a month in Cuba, my travel companion experienced seabather's eruption, which was described by Drs Mary Sy and Gary Williams in their Photo Essay "The Dermatologic Perils of Swimming" (CONSULTANT, August 2004, page 1229). Fortunately, some Cuban onlookers knew how to treat this condition (referred to locally as "El Caribe") (Figure). After vinegar was applied to the eruption, the pruritus and burning diminished almost immediately.
— Laurie Brebrick, APRN-BC
Although no published controlled studies have demonstrated that topical application of vinegar ameliorates the symptoms of seabather's eruption, there are frequent anecdotal reports of its effectiveness. Moreover, vinegar has been studied as a palliative treatment for the stings of other species of jellyfish, and data extrapolated from these studies support the use of vinegar to relieve the symptoms of seabather's eruption.1
The probable mechanism of action is that the acidity of the vinegar neutralizes the effects of the toxins injected by the jellyfish nematocysts. Interestingly, there are also anecdotal reports that a paste of baking soda and water (which has an alkaline pH) may provide relief.
Caution swimmers not to use vinegar to try to remove the jellyfish larvae from the skin immediately after they get out of the water. That practice may only serve to trigger the envenoming barb-firing mechanism and precipitate the eruption! The soothing effect of the acidic vinegar or alkaline baking soda paste comes from neutralization of the venom after it has penetrated the skin.
— Gary P. Williams, MD
Associate Professor of Pediatrics
University of Wisconsin