These animals are very sensitive to sunburn. They have a very thick endodermis covered with a very thin epidermis layer that acts like a wick. Thus they get dehydrated very quickly, losing water much more quickly than any other mammal. That's why they have to spend so much time in the water. Another adaptation to prevent water loss is secretion from the pores of a red oily substance that protects the skin from the sun, rather like sun block.
