Frogs and the other amphibians, such as toads and salamanders, have unique skin characteristics among vertebrates. A stained thin section of frog skin was photographed using phase contrast optics and is presented below.

Unlike fish, reptiles, or birds, most amphibians don't have tough, horny scales that function to keep out the elements. Quite the opposite, amphibian skin is delicate and permeable, allowing oxygen and water to pass through its pores. In fact, for many species, the skin is a vital respiratory organ with the underlying dermis richly supplied with blood vessels and lymph spaces.

In order to keep moist, frog skin contains glands that secrete a slimy mucous layer to protect the skin from drying out and help draw in oxygen through the skin. In the water, the mucous secretions help frogs retain a healthy balance of salt and water within their internal tissues. In many species, these glands are modified to produce toxins and other substances that will repel predators. Some frog skin toxins are being researched as potential pain medications.