Just got back and got it bad. I am pretty sure I got it snorkeling at Hol Chan Friday night. I had put sea safe on earlier in the day, but wore a tank top with my suit than evening. Didn't start getting the welts until Sunday morning. My whole chest area, some on my neck and abdomen. I have a steroid crème to help with the itching, and took some benadryl this morning. Pretty uncomfortable, but at least it didn’t break out until we got back, would have been miserable in the heat and sun. Will be starting a new post with some questions, like duration, spreading, etc. Will post a trip report (was all good) as soon as the itching stops !!