I’ve heard of the existence of these mites on odd occasions for decades, but have only just got some hard information on them. If you are of a nervous disposition, look away now!
Below is a classic model of our skin. You can see a hair follicle on the left & 2 sebaceous glands (vertical yellow tubes) which produce sebum (the oily stuff that keeps our skin moist). The surface of the skin is at top:-
What they never told me at school is that there are little--in fact, almost microscopic (0.3–0.4mm (0.012–0.016 in) long)--mites that live within those follicles & glands. Here is a photograph of the ones that live within the hair follicles:-