Sea Lice (Seabather's Eruption): The Itchy Rash After Swimming in Arugam Bay

A traveler comes in convinced their guesthouse has bed bugs, because they’re covered in an itchy rash under their swimsuit line. Nine times out of ten, when the pattern matches areas that were covered by togs, rash vest, or boardshorts while they were in the ocean, it isn’t bugs at all. It’s sea lice, more accurately called seabather’s eruption, and it has nothing to do with lice.

What “sea lice” actually is

Despite the name, this isn’t a louse or an insect. It’s a reaction to the microscopic larvae of certain jellyfish and sea anemones that drift in warm coastal water, particularly after calm, warm spells. The larvae are too small to see or feel while you’re swimming. The problem starts when they get trapped between your skin and your swimwear, rash vest, or wetsuit. Pressure, friction, and your body heat trigger the larvae to release their stinging cells, and you end up with a rash exactly where your clothing was tight against your skin — waistband, underarms, chest, and the backs of the legs.

This is different from a normal jellyfish sting, where the tentacle brushes exposed skin and you feel it immediately. With seabather’s eruption, the rash usually doesn’t show up until hours after you’re out of the water and have showered, dried off, and gone about your day — which is exactly why people blame their bedding or clothing instead of the ocean.

Symptoms

• An itchy, prickly, or stinging sensation that starts anywhere from thirty minutes to twelve hours after swimming
• Small red bumps or raised spots, sometimes with tiny blisters, concentrated under areas covered by swimwear
• Itching that can be intense, worse at night, and lasts anywhere from a few days to two weeks
• Occasionally mild fever, chills, nausea, or a general unwell feeling in the first day or two, especially in children or with a large area affected

The rash itself looks a bit like a cross between hives and an allergic reaction — and in a sense, that’s exactly what it is: your skin reacting to venom from dozens of tiny stinging cells rather than one sting.

What to do

1. Get out of your wet swimwear as soon as possible. Don’t rinse off in the shower while still wearing it — this is one of the most common mistakes. Fresh water running over trapped larvae can trigger them to sting more, the same way it can with jellyfish nematocysts.
2. Remove your swimwear carefully and rinse the affected skin with seawater first, then wash with soap and fresh water once the swimwear is off.
3. Don’t scrub the area. Friction is what set this off in the first place.
4. Wash your swimwear properly — a normal hot machine wash with detergent, not just a rinse — before wearing it again. Larvae can survive in damp swimwear and cause a repeat reaction.
5. Use a cool compress and calamine lotion or 1% hydrocortisone cream for itching and inflammation.
6. An oral antihistamine (such as cetirizine or loratadine, available at any pharmacy here) helps with the itch, especially at night.
7. Paracetamol for discomfort or any mild fever.

Most cases settle on their own within a week to ten days with this kind of basic care.

When to come and see us

• The rash covers a large area of the body, especially in a child
• You develop a high fever, vomiting, or feel genuinely unwell rather than just itchy and uncomfortable
• The bumps become infected — increasing redness, warmth, swelling, or pus, which can happen with the scratching that inevitably follows a rash this itchy
• Over-the-counter antihistamines and hydrocortisone aren’t controlling the itch after a few days
• You’re not sure whether what you’re looking at is actually seabather’s eruption, a different skin reaction, or something else — reef cuts, sandfly bites, and heat rash can all look similar under a rash vest line, and it’s worth letting us take a look rather than guessing

We can prescribe a stronger topical steroid or, occasionally, a short course of oral steroids for severe reactions, and we’ll check for secondary infection if the skin has been scratched open.

Prevention

There’s no foolproof way to avoid it if the larvae are in the water, but a few habits reduce your odds:

• Shower and change out of swimwear promptly after swimming, rather than lounging around in a wet rash vest for hours.
• Avoid swimming in visibly murky or churned-up water after storms, when larvae tend to be more concentrated near the surface.
• Rinse swimwear in fresh water and wash it properly between wears, not just a quick rinse and re-wear the next day.
• If you’ve had a bad reaction before, some travelers find a thin layer of a barrier-type sunscreen or surf lotion on the skin under swimwear reduces how often they react, though this isn’t guaranteed.

Seabather’s eruption tends to come in waves locally — if one swimmer in your guesthouse gets it after a session, others who were in the water at the same time and place often will too. It’s not contagious between people; it’s simply that you were all swimming in the same patch of water at the same time.

Related reading

• Jellyfish Stings on Sri Lanka’s East Coast: First Aid That Actually Works
• Prickly Heat in Arugam Bay: Why It Happens and How to Clear It Fast
• Allergic Reactions in Sri Lanka: Recognising and Treating Them

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This article is general health information and not a substitute for medical advice. If you’re not sure what’s causing your rash, or it’s getting worse rather than better, walk in any time or call 1990 for emergency transport.