Seabather’s eruption (SBE) is a common skin condition for ocean swimmers. It is a type of dermatitis, sometimes incorrectly called “sea lice,” caused by the microscopic larvae of thimble jellyfish or sea anemones. These larvae become trapped against the skin, triggering an immune reaction to their stinging cells. This information clarifies the typical duration and effective management of SBE.
Identifying the Cause and Symptoms
Seabather’s eruption is caused by the larvae of Cnidarian species, primarily the thimble jellyfish (Linuche unguiculata) or, less commonly, the sea anemone (Edwardsiella lineata). These tiny, almost invisible organisms float in the water and easily pass through swimsuit fabric. They become concentrated against the skin as the swimmer exits the water, where they possess nematocysts, which are specialized stinging cells containing venom.
The stinging cells are triggered to fire by mechanical pressure, such as swimsuit fabric rubbing the skin, toweling off, or exposure to fresh water. The discharge of venom and the body’s subsequent immune response lead to the eruption. The rash is characterized by small, red, intensely itchy bumps (papules) that often appear hours after leaving the water.
The rash is typically concentrated in areas covered by swimwear, where the larvae were trapped, but it can also occur in hair or areas of friction. SBE should be distinguished from “swimmer’s itch” (schistosome dermatitis), which is caused by parasites found in fresh water and affects only exposed skin. Generalized symptoms like fever, chills, headache, or fatigue may accompany the rash, especially in children.
The Typical Duration and Recovery Timeline
The onset of symptoms usually begins within minutes to 12 hours after initial exposure. The severity and duration of the rash are influenced by the concentration of larvae encountered and the individual’s immune response to the venom.
For most mild to moderate cases, the eruption resolves within 1 to 2 weeks. The most intense itching and rash commonly peak within the first 2 to 3 days. Individuals with a history of previous exposure or heightened sensitivity may experience symptoms that persist for several weeks.
In rare, severe instances, symptoms may take up to one or two months to clear completely, especially if excessive scratching leads to a secondary bacterial infection. Medical consultation is recommended if the rash shows signs of infection, such as increased warmth, pus drainage, or red streaks, or if systemic symptoms like a high fever persist. If the eruption has not significantly improved after two weeks, a medical professional should be consulted.
Immediate Relief and Treatment Options
The first step after suspected exposure is to immediately remove the contaminated swimwear, ideally before rinsing the body with any water. Removing the suit prevents remaining larvae trapped in the fabric from discharging more nematocysts onto the skin. Applying a household solution like diluted vinegar or rubbing alcohol to the affected skin may help neutralize residual toxins on the surface.
Treatment for the rash itself is focused on managing inflammation and intense itching while the body recovers. Over-the-counter 1% topical hydrocortisone cream should be applied two to three times daily to reduce inflammation and discomfort. Oral antihistamines, such as diphenhydramine or cetirizine, can be taken to control the allergic reaction and alleviate severe itching.
Cool compresses or ice packs wrapped in a cloth can be applied to the affected areas for temporary relief from itching and burning. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen may manage general pain and inflammation. Avoiding scratching is paramount, as broken skin significantly increases the risk of developing a bacterial infection.
Preventing Future Outbreaks
Preventing recurrence involves minimizing contact with the larvae and implementing specific post-swim practices. Swimmers should check local health reports and avoid swimming during peak seasons, typically March through August, with high incidence in May and June. Since larvae are most prevalent near the water surface, swimmers and snorkelers are particularly susceptible.
Immediately upon exiting the ocean, all swimwear should be removed. The body should be rinsed with clean seawater if possible, before showering with fresh water. Since fresh water can trigger the stinging cells, showering with the contaminated suit still on must be avoided. After use, all exposed swimwear must be thoroughly washed with detergent and dried, preferably with heat, as air-drying may not deactivate trapped nematocysts.
Wearing two-piece swimsuits instead of one-piece suits or t-shirts may reduce the surface area where larvae can become trapped. Some swimmers use protective lotions or specialized sunscreens that are marketed to prevent stings by inhibiting nematocyst discharge, though their effectiveness varies. If a severe reaction has occurred, individuals may choose to discard the infested suit altogether to eliminate the risk of re-exposure.