Oxygen is essential for life and it has to be obtained from somewhere to supply every cell of the organism with it. Most animals on our planet take oxygen from the ambient atmosphere or breathe oxygen dissolved in water. They breathe through the lungs or gills, from which the oxygen is distributed to all parts of the body.
At first sight it may seem that the most difficult task is to obtain oxygen from water or the atmosphere, but this is not so. Animals did not have to invent any special mechanisms. Oxygen enters the blood through the lungs or gills by diffusion since the blood contains less oxygen than the environment, and gases and liquids tend to distribute themselves equally within the limits of any enclosing walls.
Nature did not hit immediately upon the idea of lungs or gills. These organs were virtually unknown in the earliest, multicellular, living organisms, which breathed with the entire surface of their body. All the subsequent higher-developed animals, man included, have evolved special organs, intended for respiration, at the same time retaining their capacity to breathe through the skin. Only armour-clad creatures, such as turtles, armadilloes, crabs, and the like, are unable to breathe through the skin.
In man breathing involves the entire surface of the body, including the thickest skin on the heels and the hair-covered scalp. The parts of the skin that breathe most intensively are those on the chest, back and abdomen. It is worthy of note that these parts of the skin breathe more intensively than the lungs. If we take two equal sections of the breathing surface of the skin and the lungs, we will find that the skin can absorb 28 per cent more oxygen and expel as much as 54 per cent more carbon dioxide than the lungs.
The skin’s superiority is very difficult to account for. One possible explanation may be that the skin breathes clean air, while our lungs are inadequately ventilated. Even after a very deep expiration some air remains in the lungs; the composition of this air leaves much to be desired: the oxygen content in it is much lower than that of the atmospheric air, while the carbon dioxide content is much higher. The air inhaled during inspiration becomes mixed with the residual air in the lungs, and its composition deteriorates. It would not be surprising if this were the phenomenon that gives skin breathing the advantage.