MAMMALIAN life—in sea, fresh water, or air—could not exist should the outer integument—the skin—be permeable to water, inorganic ions, and gases.
The removal of more than 30% of the integument from a terrestrial mammal living in dry air at a temperature lower than 28 C kills the animal by imposing such a negative evaporative thermal load upon the organism that it exceeds the organism's capacity to generate enough heat from exothermic chemical reactions to maintain body temperature. The body temperature drops and the animal dies.6
The burned human being bearing a granulating wound larger than 20% of body surface, if immersed in water, becomes ill and even dies of a combination of water gain and salt loss.
Obviously such mammals as the whale and porpoise living in hypertonic seas could not exist should their skins not be impermeable to salts as well as water. Their sole water source is
MOYER CA, DILLON JS, BUTCHER HR. Function of Human Skin in Relation To Its Macromolecular Structure. Arch Surg. 1966;92(2):222-242. doi:10.1001/archsurg.1966.01320200062011