Many swimmers encounter an irritating skin rash after spending time in the ocean, commonly referred to as “sea lice” stings. This uncomfortable condition, more accurately termed “seabather’s eruption,” is not caused by actual lice, which are parasites that affect fish. Instead, the rash results from contact with the microscopic larvae of jellyfish, particularly the thimble jellyfish (Linuche unguiculata), and sometimes sea anemones, floating in the water. These tiny marine organisms, often no larger than a pinhead, carry stinging cells that trigger an immune response upon contact with human skin.
Identifying Sea Lice Stings
The hallmark of seabather’s eruption is a rash that typically manifests as small, intensely itchy red bumps, sometimes developing into larger hives or welts. A telltale sign is the rash’s distribution, appearing predominantly in areas covered by a swimsuit, wetsuit, or even hair, as these materials trap the microscopic larvae against the skin. Pressure, friction, or exposure to fresh water while still wearing contaminated swimwear can cause the larvae to discharge their stinging cells, known as nematocysts, releasing toxins. While some individuals may experience a tingling or prickling sensation while still in the water, symptoms usually emerge several hours after leaving the ocean, often within 4 to 24 hours. Children may experience additional systemic symptoms like headaches, nausea, or fever.
Immediate and At-Home Care
Immediately upon exiting the water, remove your swimsuit to prevent further larvae from becoming trapped and discharging toxins. Rinse your body thoroughly with fresh water, then wash the affected skin gently with soap and water to dislodge any remaining larvae and their stinging cells. Applying diluted vinegar or rubbing alcohol to the stung areas may help to inactivate any undischarged nematocysts on the skin, although this will not prevent the rash’s onset.
For localized itching and inflammation, over-the-counter 1% hydrocortisone cream can be applied to the rash a few times daily, providing relief. Oral antihistamines, such as diphenhydramine, can also be taken to reduce the body’s allergic reaction and alleviate widespread itching. Calamine lotion offers soothing relief for irritated skin, while cool compresses or ice packs applied to the affected areas for 15 to 30 minutes, several times a day, can help reduce pain and swelling. Avoid hot showers or baths, and direct sunlight on the rash, as heat can worsen the itching.
When to Seek Medical Attention
Most cases of seabather’s eruption resolve with home care, but seek medical attention if the rash persists for more than one to two weeks, or if it becomes extremely painful, covers a very large area of the body, or shows signs of worsening. Signs of a secondary infection from scratching, such as increased redness, warmth, swelling, pus drainage, or red streaks extending from the rash, also warrant a doctor’s visit. Systemic symptoms like a high fever, chills, severe nausea, vomiting, or extreme weakness also require consulting a healthcare provider. A doctor might prescribe stronger topical or oral corticosteroid medications to manage more severe reactions.
Preventing Future Stings
Always heed any posted warnings at beaches regarding jellyfish larvae or “sea lice” outbreaks, as these indicate periods of higher risk. Consider avoiding wearing t-shirts or one-piece swimsuits while swimming in affected waters, as these garments can trap a greater number of larvae against the skin compared to more minimal swimwear. Shower immediately after leaving the ocean, ensuring you remove your swimsuit before rinsing with fresh water, as freshwater contact can trigger the stinging cells. After each use, thoroughly wash all swimwear with hot water and detergent, then machine dry it to ensure any lingering larvae or their stinging cells are completely removed.