Seabather’s Eruption (SBE) is a skin condition caused by exposure to specific marine larvae in ocean water, often incorrectly called “sea lice.” While intensely irritating and uncomfortable, the reaction is generally benign and resolves without long-term consequences. The rash is a localized hypersensitivity response that is highly bothersome but rarely poses a serious threat to health.
Identifying the Cause and Symptoms
The cause of SBE is exposure to the microscopic larvae of Cnidarians, primarily the thimble jellyfish (Linuche unguiculata) or, less frequently, the sea anemone (Edwardsiella lineata). These larvae become trapped against the skin, especially in areas covered by swimwear. The reaction is triggered when the larvae’s stinging cells, called nematocysts, are discharged.
This discharge occurs when the larvae are stressed by pressure, friction, or exposure to fresh water, not in saltwater. Symptoms typically begin a few hours after leaving the water, presenting as a highly pruritic, intensely itchy rash. The rash consists of small, raised red bumps or blisters (papules) that appear in the pattern of the clothing.
Assessing the Risk and Severity
While SBE is localized to the skin in most adults, it can cause systemic symptoms indicating a more severe reaction. These signs include fever, chills, headache, nausea, vomiting, and a general feeling of illness. Fever onset is disproportionately high in children under 16, affecting up to 40% of younger patients compared to 10% of adults.
The condition is rarely dangerous, but complications arise if intense itching leads to excessive scratching. Scratching breaks the skin barrier, creating openings for bacteria and leading to a secondary skin infection. Individuals with pre-existing skin conditions, such as eczema, or those who are immunocompromised may experience a prolonged reaction. Medical attention is necessary if the rash shows signs of infection (increased warmth, pus drainage, or red streaks) or if severe systemic symptoms like breathing difficulty or persistent vomiting occur.
Immediate Relief and Management
The immediate priority after suspected exposure is to remove contaminated swimwear without delay. Larvae remain trapped in the fabric, and further friction or fresh water can cause additional nematocyst discharge. Before showering, rinse the affected skin and swimsuit with seawater, vinegar, or rubbing alcohol to neutralize any undischarged stinging cells.
Once the rash appears, treatment focuses on relieving intense itching and inflammation. Over-the-counter oral antihistamines, such as fexofenadine, help manage the pruritus. For the localized rash, applying a topical corticosteroid cream (typically 1% hydrocortisone) two to three times daily reduces inflammation. Avoiding scratching is necessary to prevent bacterial infection.
Prevention Strategies
Preventing SBE involves avoiding exposure to the larvae, which are most prevalent during late spring and early summer, typically peaking in May and June. Swimmers should monitor local beach warnings and advisories, especially in endemic areas like the Caribbean and the coast of Florida.
The most effective preventative measure is changing out of the swimwear immediately upon exiting the ocean, rather than showering while wearing the suit. Since fresh water triggers the nematocysts, showering with the suit on drives the stinging cells into the skin. T-shirts and one-piece swimsuits may trap more larvae, increasing the risk. After exposure, contaminated swimwear must be washed in hot, soapy water and dried thoroughly to kill residual larvae.