We have been on two cruises and spend two entire days in the water at CC ant no one in the family (4 total) has ever had a problem, we never bought any special products (in fact, I had never heard of sea lice before reading these boards in prep for our second cruise) although we do always wear sunscreen if that makes a difference. It is also something that I never heard anyone on either of our cruises discussing as a problem. I am sure that some people have had trouble or if wouldn't be such a big discussion topic, but I wouldn't worry yourself too much about it.