In FL we call it sea lice. Certain people are more prone to it, my middle daughter gets it the worst. The one thing they tell us down here is to make sure you rinse off with fresh water a ton after you get out of the ocean - especially where your swimsuit touches or covers you as that is where they get you the most. My daughter does rinse off, but she is my biggest swimmer so she stays in the ocean forever before she runs to the showers.