Sea lice: That nasty rash you get after swimming in the ocean

Sea lice, the likely reason you’re itching after swimming in the ocean

Have you ever been ocean swimming and felt like you’ve got an itchy bite? or come out in a rash after open water swimming?

The chances are it’s the result of what’s commonly referred to as ‘sea lice’.

In fact, it’s not ‘sea lice’ or ‘sea louse’ in the way fishermen might think of it. This type of sea lice/louse is a marine parasite that affects fish by feeding on the mucus, epidermal tissue, and blood of host marine fish, and actually have nothing to do with the itchy rash you’ve experienced.

Sea louse, (the marine parasite version) was also thought to be responsible for the bleeding legs of a swimmer at Brighton in Melbourne – this is not the type of sea lice that this article refers to.

A red itchy looking sea lice rach on the torso of a swimmer.
Example of sea lice rash, in this case predominately in the area under bikini strap where sea lice have been trapped.

What is sea lice?

‘Sea lice’ that cause ‘itchy bites’ are tiny little jellyfish or stinger larvae that have the same stinging cells (nematocysts) as an adult jellyfish/stinger, but because they’re only small they only affect a small area.

They tend to travel in large groups or ‘blooms’ and will be prevalent in warm summer waters – some ocean swimmers suggest you’ll encounter them when there is lots of seaweed floating around.

How do sea lice cause the itch?

Sea lice are microscopic and transparent in water so you’ve got no chance of seeing them, the first you’ll know about it is when you start to itch.

You’ll get the worst of it where the larvae get trapped under your swimsuit or rashie, or even under your armpit where they feel trapped causing the stinging cells to fire.

Sea lice treatment

  1. The worst thing you can do is itch the itch, you’re best to just flush your skin in freshwater when you get out – preferably with your swimsuit removed.
  2. When drying yourself off use a patting motion rather than rubbing the affected area.
  3. For the majority of people, the itch will be the worst part, and it could be delayed and last for a few days to a week after.
  4. For some people, it could get worse with a severe reaction, in which case you should seek further medical assistance.
  5. Give your swimsuit a good wash (try soaking in boiling water) before you wear it again just to make sure all the cells have been washed out.
  6. If you’re looking for relief treatment try vinegar, various ‘itchy bite’/rash/sting creams, steroid creams or antihistamines – but check with your doctor first. Other remedies include tea-tree oil and ice packs to help cool the heat in the rash. (See comments below for reader suggestions)

First published in February 2012

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  1. Just got a nasty surprise of sea lice stings while snorkling in Haiti. Really painful for the first 24 hours and then just really itchy. Oh yeah, and ugly looking too! My back is covered where bathing suit band was, as well as arm, waist, and neck. Happened 5 days ago and it’s becoming the gift that keeps on giving.

  2. I have them and they are really itchy but you must not itch them because they get worse and I have them on my belly and a some on my back and arm.

  3. Is it normal to get them all over your body?
    I was free diving yesterday afternoon and now my hole body has small little dots and rash like symptoms.

  4. Thanks Andre, a very informative and simplistic explanation of what sea lice are. I didn’t realise they were actually a type of jelly fish so makes sense to use vinegar on the rash. I have them and received one lot on one arm then a few days later had another swim thinking the sea water would help the rash (not realising the rash was from sea lice) then gained another rash on the other arm which looked different. I am using Urticara Urens as homoeopathic and now Apple cider vinegar. Many thanks D.

    1. Thank you Diane, I ran through a thinks pile of seaweed that covered the usual sand where I sometimes run and had the worst case of this a year ago. Then I wore the (washed!) socks I’d worn that day recently and again it occurred, including an unpleasant allergic reaction. Your use of apple cider vinegar has saved me from going crazy. The socks will follow the shoes into the bin.

    1. Hi Barb, the rash shouldn’t really spread if you’ve washed your body in fresh water (remember to pat yourself dry, not wipe). You should also make sure you wash your swimwear before wearing again – same goes for any clothing you may have worn after your swim. If your rash gets worse you should see a doctor. I hope that helps, and you feel better soon!

      1. hi! I know you said they shouldn’t spread out, but mine has. I got the first rash six hours after coming home from the beach this past Monday, and I’ve been getting them all over my back ever since. Today, I saw another rash on my thigh, and it really creeped me out. How long will it take for them to vanish? Thank you

  5. I wore my bathing suit 1 week ago in the ocean but no bites and then again yesterday and noticed a cluster of bites where one of my bikini straps was. I did not was the bikini top inbetween uses. How long can they survive on swimwear after initial contact?

  6. My daughter contracted sea lice the other day swimming at Lake Worth beach where was a lot of sea weed, and she was red all over her body. I prepare her bath with camomile tea (i cooked around 8 bags of tea and poor it in the bath water). Then i put very greasy children’s cream on her. She is much better today.

    1. Hmmm, not sure the answer to that one. I might suggest that if you were severely allergic then you’d experience a reaction pretty quickly. Always see a doctor if you are in any doubts.

      1. Andre, I found your explanation and advice really helpful. I now suffer from severe allergic reactions to stingers, I’m predisposed I guess, because I react also to simple mosquito bites. Thankfully, I’ve avoided bee stings. My reaction to marine stingers is almost immediate, and within half an hour is severe. The welts come up, and then blisters form (bullous] and the itch is strong. The pain from the sting is only momentary. It’s the itching and swelling that becomes a problem, and for me the blisters can last for a week or two. The scars last for a long time, but eventually disappear. I’ve tried rashies for protection, even doubling, but that doesn’t work for me, so it’s a westsuit vest now (long arms]. So far the legs haven’t been hit, but if they do, then it will be a full wetsuit just so I can keep swimming. I take an antihistamine until the swelling stops, and steroid cream till the blisters subside. Hope this information helps someone else.

  7. Hi, went swimming and next morning had these “bites” on my body. After this I’ve cleaned everything and tried not to scratch like you said but the marks keep on appearing and disappearing. Same place different places. It’s like it can’t decide where to flare up. I this normal?

  8. Our daughter has just been told she has been bitten by sea lice. we are at Umina on Holidays. She has been given antibiotics to take and we will see how it goes. She was bitten around the right ear area.I was going to attach some photos but not sure how. Thanks

    1. Hi Craig, that doesn’t sound nice for your daughter at all! It’s very interesting to hear that she was given antibiotics for it, it must have been some rash! You could send photos to [email protected], we’d love to see them and we can add them to our stock photos to show others what sealice rashes can look like. All the best to your daughter. Andre

  9. We live in Aruba and you hardly see any sea weed, but these days with all the hurricanes around the Caribbean the beaches look a little different and with some sea weed. My wife went in the water and a few minutes later it started itching and getting red around her inner thighs. Thanks for your comments they helped a lot in knowing what to do.
    Your comments were very helpful to know what to do

  10. In Costa Rica and got a nasty allergic reaction under armpit after carrying board from beach w/o rash guard. It WAS a green tide too….

  11. Got a very itchy rash on ribs and back the day after doing Cronulla swim. Rash looks like sealice rash. Can the sealice survive out of water?

    1. Hi Sue, a few people have run into sea lice at ocean swims over the weekend. Sea lice will continue to ‘sting’ out of the water, and you’ll need to wash them all off, and out of your clothes to get rid of them. See all the advice in this article, and from people’s comments.

      1. I get sea lice bites, at least I think they are every time I go in the ocean. Except no one else does. I get them on my stomach, Chest, thighs, and arms but I’m the only one! Even with a brand new suit. They resemble never ending itch mesquito bites. Please help! I try not to itch them and apply creme.

  12. Greeting Andre,

    This comment is left for your opinion on a diagnosis and the long term side effect to my condition(if applicable). In concerns to a narley rash I received during a trip to the Caribbean.

    Took a swim off a beach in Sint maarten, came out with 4 rashes and a swollen p***s.
    Each rash was on each limb, on the crook of my elbows and knees

    I just rinsed my body off in the shower head on the beach and a local magically made appear a limb of Aloe Vera to rub on my rashes.

    Do you think I may have contracted a disease or parasite that is now dormant in my body.
    If not treated could the issue get worse or life threatening over time?

    Thank you,

    1. Hi Devin, I’d suggest seeking medical attention if you believe your condition is beyond the usual signs and symptoms of sea lice as described here. All the best.

  13. I was swimming at the beach a couple years back and suddenly I felt an itch and burn in my upper inner arms (just before my armpit) and saw that I had a little patch of red on both arms. I still have the marks but they get inflamed in salt water. What is it?

  14. Every swim I get bitten. I feel the little pricks when I’m swimming and guaranteed that night I’ll have a rash and itch. I takes a lot of will power not to scratch. I tend to take a sleeping pill on the first and second night. Apply ice packs and cream and by the third day the itch is gone but the spots stay for another few days. I then repeat the cycle the next week. I may need to pick another hobby :-/

  15. I windsurf at Kyeema near the airport in Botany Bay (Sydney). I’ve grown used to always getting a few “bites” each time: they tend to come up about 24hrs after each swim, and last three or four days, even though I rinse thoroughly using soap as soon as I come out! Stinger suit no help: I’ve just learnt to put up with it, as the spot is too convenient for me!! Stingose mildly helpful, probably because I stop scratching when I put it on!! Of course it could be the heavy metals and other obnoxious stuff from the George’s River outfall … although it’s quite exiting to look down and realise you are over a carpet of jelly blubbers … and some one has just seen a white pointer or bull shark 300 yards down the beach …

  16. Why would i be the only one in my group who swam together to get these rashes? I did rinse in fresh water afterwards

  17. Swam at Little Bay on Thursday 7/2 and now have a sea lice rash. Found comments and recommendations helpful. Thank you. On Thursday there were a lot of young small jelly fish in the water.

  18. @Claire

    You described pretty well what happens to me. If I am not wearing a head to toe wet suit, my face and lips will still get stung. I went snorkeling in a bikini recently in Thailand through corals and came out with my neck shoulders and upper back cover in welts. I immediately went to the pharmacy got cream and antihistamines… I believe some people are more sensitive than others because I am the only one in the group to get stung.

  19. My daughter was with 5 others in the water. She is the only one that has the stings? Is there a reason why?

  20. My friend Sheila was in St. Martin a year ago and contracted a rash on her back & arms. It’s better than it was last year, but the itching still drivers her crazy on her back & arms. From what I’ve read, I can’t decide if it’s sea lice, scabes, or what. The lesions haven’t broken out anywhere but her upper back and upper arms. Any help would be appreciated.

  21. Thanks for sharing this, I just had it recently and I’ve had a few years ago both times in places where my wetsuit or rashly have trapped them.

  22. do ‘sea-lice’ bites become blisters? I have about a hundred of them after going into warm shallow water at Central Coast, NSW.

    1. I haven’t come across this before, so maybe you should visit your doctor to have them checked out. The only thing I could think of is if you’ve been itching/rubbing them so much you’ve rubbed the skin raw?

  23. I live on the coast and swim 2-4x/ day. Sea lice reactions are odd.Two years ago a friend near by had it bad. I had none. This year I have it and he doesn’t.

    I splash my infected arm pit areas with fresh water then vinegar when I get out. Seems to help but now it is lightly spreading to upper leg near groin.

    My friend used dollar store cooking oil on it and it finally went away after he jad it for a few months (maybe the season ended I wonder).

    I sometimes use coconut oil which nourish the skin and eliminates the rare itching. Found an essential oil blend I use for anti mosquito bite and swelling seems to make sea lice reaction worse. It’s so confusing, all I know os swimming is a art of my life and it will not keep me out of the water unless sea grass cover is heavy.

  24. I’m having it right now, it started when we get back from the beach last Sunday. It’s not itchy but sore, what should I do? Or what home remedy can I do to reduce this? Thank you

    1. It’s fine to go back in, it might even take your mind off it. Either way, you’ll find out whether it’s enjoyable or not to go back in.

      1. HI Andre, all the articles I can find about sea lice seems to be saying they are prevalent in warm water, however I’m sure I’ve been biten in super cold waters in Perth, Western Australia yesterday as I have an itchy rash all over where my bathers were. I’ve had sea lice rash before in the Caribbean so remember what it felt like. Do you think it could also happen in cold waters?

        1. Hi Jessica, it’s definitely possible you’ll find them in cooler waters. If it looks like a sea lice rash and feels itchy like a sea lice rash, there’s a good chance it’s a sea lice rash.

  25. Thank you. That explains it. I went bodyboarding in Waikiki by the wall/graveyards and afterwards got these tiny bites all over my upper body. It’s so itchy. I’ll try apple cider vinegar

  26. Hi this is so interesting. I’ve been searching for some help.
    My 10 year old daughter in the last 2 years gets rashes when she’s in the sea, under her arms usually. We are from the UK but here she wears a wet suit as it’s so cold and doesn’t seem to be effected so much. But our trips to Florida she now has issues and we went to Turkey in August and the same problem. It seems to be quite a recent allergy for her.
    Maybe antihistamines before she swims and a wetsuit top may help?

  27. Very common in Bundaberg.

    You notice them a lot if you go spearfishing without a wetty.

    Not much you can really do except grin and bear.