A frog is compleately covered by a soft, thin and moist layer of skin make of two very important layers, the epidermis and the dermis.
It does not really protect the frog in any way but, it helps in the process of respiration. Oxygen can actually pass through a frog’s skin, which then enters into their blood.
Frogs dont only breathe though their skin, some adult frogs have two sac-like lungs.
When a frog is sumerged underwater, its respiration takes place through their skin only.
There are many blood vessels that run throughout the frog’s skin. Oxygen can actually pass through it, therefore, it directly enters into the blood. Oxygen can be gotten from water too.