The human body is home to trillions of microorganisms, from bacteria to fungi. Some of these perform useful functions for us, like the flora living in our gut that aid gut development and help train the immune system. Even those that have no effect aid us just by being there - they compete for resources with harmful microorganisms like C. difficile, limiting their growth.
The yellow column in this photo is a hair, and the green objects are tails.
This is a photo of the face mites that live in your eyelashes, eyebrows and hairs in your ears.
Demodex folliculorum and Demodex brevis measure around 0.03-0.04mm and live for about two weeks. They are more commonly found on older people than children, as older people produce more sebum (an oily substance produced by the skin to lubricate and waterproof it), which they feed on. They assume a head-in tail-out position in the follicle, but remain able to move between follicles. Though a minority of people can get reactions such as inflammations, most people live in unknowing harmony with these guests.
Sources: 1 & 2