Amphibians absorb oxygen through their moist skin during cutaneous respiration. Oxygen dissolved in air or water diffuses across the thin skin and into the dense network of capillaries beneath it, while carbon dioxide diffuses outward.
Moisture is essential because gases cross the skin in solution. Amphibian skin contains mucus glands that help prevent drying, and many species rely more heavily on skin breathing in cool water, at rest, or while submerged. Some lungless salamanders use cutaneous respiration as their only form of gas exchange.
The process does not mean amphibians breathe only through their skin. Frogs may also use lungs and the lining of the mouth, while larvae commonly use gills. The word “respiration” here refers to gas exchange, not cellular respiration inside the body.
A striking specialist is the hellbender, whose wrinkled lateral skin folds enlarge the respiratory surface; cutaneous exchange supplies more than 90% of its oxygen uptake. Hydrogen, methane, and nitrogen are not the respiratory gas sought in this context.