The skin of a frog has two primary functions: helping the frog to drink and helping the frog to breathe. Toads also use their skin in these two ways, though they are able to retain moisture better than frogs and do not need to be as close to a water source.
It is important that each frog maintain a proper level of moisture in their skin in order to breathe. Without this level of moisture, the frog can suffocate and perish. The frog uses its skin as well as its lungs and mouth lining in order to breathe. When the frog is underwater, it uses its skin only to breathe by allowing gasses to permeate the body as well as leave it. When out of the water, the frog uses mucus glands to dissolve oxygen that is already present in the air and then to absorb it. Frogs also need to be able to breathe whenever they are hibernating and breathing through their skin is the only option when they are buried in mud for hibernation.
The frog also uses its skin to drink because frogs do not drink water or other liquids through their mouths. The frog has a patch on its stomach and part of its thighs where it can absorb water. These areas are commonly referred to as the "drinking patch areas."