"rash" from beach?

[Cat714]

I went to the beach today, and as soon as I got out of the ocean, I noticed a multitude of raised red welts (ranging from the size of a pen-tip to the size of a tic-tac) scattered about on my thighs and calves. They appeared nowhere else on my body. It is not razor stubble (I do not need to shave my legs above my knees, so I never have), and this "rash" (?) does not itch or hurt, unless I press one of the welts, in which case it has the same abrupt and quickly-passing stinging feeling as pressing on a mosquito bite. I swam in the ocean a few more times today, and they didn't seem to get better or worse. Some of them are fading in color (it's been five hours), but the skin is still raised. I did not see any jellyfish in the water, or seaweed, and it did not hurt or sting. Any idea what this might be? Thank you!

[Bhupinder Kaur, MD]

Hello,
Thanks for posting your query.

From your symptoms it looks like sea lice bites. The other possibility would be swimmer’s itch which is a short-term, immune reaction occurring in the skin of humans that have been infected by water-borne schistosomatidae.

Sea lice are most active between April and August and are often found in US sea water. There is nothing to worry. Just take a bath with Aveeno oatmeal and apply calamine lotion on the rash. Also wear cotton clothes and take some anti inflammatory drug like Diclofenac or Ibuprofen.

Hope that this information helps and hope that you will get better soon.

Wishing you good health.

[Cat714]

It is the following afternoon, and the rash (?) is still there. I have noticed a few other similar red dots on parts of my arm and hands, but they are nowhere near as numerous or bright as the ones on my thighs and calves. What sort of a reaction could this be?! I am not allergic, somehow, to the ocean am I? Is that even possible?