So basically, water is lost as a result of this process of diffusion that takes place through the skin. And this is different than sweating. So, once again, the skin is an excretion organ as well as a secretion organ. It can excrete water to the skin surface via diffusion. Waste products such as urea, salt, such as sodium and water can all be excreted via the process of sweating, as well as via trans epidermal water loss. Now, function number five is that in immunity.