Amphibians have a specialized method of breathing through their skin called cutaneous respiration. This type of respiration takes place through the skin. The skin of toad is very thin and enriched with blood capillaries. The skin of toad contains a large number of mucous glands. Mucus is discharged from these glands; as a result, the skin remains moist. For this reason, exchange of oxygen and carbon dioxide take place through the skin easily in the process diffusion.
During hibernation, the toad respires by this process. Because of the dependence on water, many toads have retained the traits of their ancestors, including reduced or even absent lungs. Many rely on breathing through the skin, cutaneous respiration, for some or all of their oxygen intake, and especially for carbon dioxide output.