Wool isn't 'self-cleaning' at all. Ever seen a sheep's bum, close up? Especially after a flush of spring grass LOL!
HOWEVER - natural, even scoured, wool (BUT NOT SUPERWASH WOOL!) has several properties that give it a certain degree of stain resistance together with some anti-bacterial and anti-microbial action.
Basically, wool has a microscopically thin waxy coating, to the individual fibres, which contains fatty acids that inhibit the growth of mould (such as mildew) and bacteria. This same coating also repels water that is needed for mould and mildew to grow. As the growth of - especially - bacteria - is inhibited, the garment will still smell fresh after the sort of wear pattern which would make a synthetic garment smell really bad. Also the natural anti-bacterial coating prevents body bacteria from entering deep into the fibres and producing their own durable stink, which is all too common with synthetic 'thermal' fabrics.
As this coating repels water, it also repels many of the liquids which cause stains, which make such stains easier to clean off, by wipin or rinsing. In addition, the microscopically-scaly surface of wool fibres block more solid dirt and stains from being absorbed as particles sit on top of the fibres which means they are much easier to remove.
As if that weren't enough, wool has a natural elasticity which far outlasts that of many other fibres. This natural elasticity means that wool will retain the shape of the item it's been made up into, and as we all know, a garment which is 'in shape' looks better (and by implication, cleaner and fresher) than one which is baggy and out-of-shape.
) over my mutt when I take him in. They usually give me a fish or a sausage that's been in the hot display for a while and dried up slightly, saying "here, take this for him (dog) to have". I tend to give him some, but eat most of it myself. 
Am I bad? 
