Why is cutaneous respiration impossible?

Cutaneous respiration is not entirely impossible, rather it is inefficient. The reason behind it is the comparatively low permeability of the skin and its overall thickness. Mammals have a well-developed, specialized respiratory system that allows for efficient gas exchange, whereas they do utilize integumentary gas exchange to a certain degree.

Amphibians and some other less evolutionarily advanced organisms may practice cutaneous respiration, and they have much thinner and more permeable skin compared to mammals. It is also worth noting that in animals with cutaneous respiration, the skin may be moistened for better efficiency of the gaseous exchange.