Reptiles are covered with scales. Unlike the scales of fish, reptile scales are not individual pieces. The entire outer layer of reptile skin is like a sheet of scales.

Scales are formed from the protein keratin, which also makes up feathers and fingernails. Reptile scales keep moisture inside the animals, preventing dehydration. All reptiles do not have the same type of scales. Those of snakes and lizards overlap, while most scales in turtles and crocodiles just touch. As reptiles grow, they need larger scales. Once formed, scales do not lengthen and widen. Instead, most reptiles shed old scales. The can happen with single scales, patches or the entire skin. However, in turtles, smaller scales often attach themselves to new scales, forming ringed patterns.