Germs, Germs, Germs
There are a bunch of bacteria on your skin. Most of them are good for you, too. Some have useful functions, while other "useless" bacteria take up space that would otherwise be occupied by harmful bacteria. If you don't wash, the chances of harmful bacteria getting into your body through your eyes, nose or mouth increase - and that's how you get sick.
Besides getting sick, some bacteria and fungi can cause infections. Especially if you don't wash them away regularly.
If you don't wash, dirt, sweat, dead skin and oil will accumulate on your skin. So not only do you look dirty, it's bad for you!
If you don't wash long enough, you'll end up with brown spots on your skin. Something called Dermatitis Neglecta. DISGUSTING!
Body odor occurs when bacteria dissolve the chemical compounds in sweat. The byproducts that are formed stink! If you don't wash away the sweat and some bacteria, it will get out of control.