Wore these on a Honeymoon Vacay to Jamaica. On our first day I had some sort of strange reaction on the top of my feet. Initially thought it was sunburn but the following day it was apparent the area on my feet affected was the areas in contact with the upper of the sandal. I investigated this when I got back with Associates at a local O-Store and they'd heard similar stories so the going theory was that sunscreen and the anti-microbial treatment created a reaction of which is yet undetermined. Otherwise they were a solid choice for wet/dry, comfort and durability.