They're very intolerable to getting sick. If they do, it doesn't last long. They do need to sleep, eat, and everything. Shades are the human forms of the pure elements. And actually, the regeneration of shades can be stopped, but only in certain ways. But if it is and the shade dies, the elemental looses their power with it and the element disappears. The human bodies are actually kind of guards to keep the element safe. For example, the darkness shade is killed and does not regenerate, the darkness elemental will be an ordinary human and all darkness will cease to exist.