Hello Doctor. My 17 year old son went for a swim in the Florida Keys ten days ago and shortly after, emerged from the water complaining that the palms and fingers of both hands were itching and painful - with the exception of his thumbs. I gave him a Benadryl, and the symptoms subsided, only to re-emerge a week later (yesterday) with painful itching and slight swelling. He did handle some rocks, seaweed and sand underwater, but has never exhibited any reaction to these things before. Please help!!