Demodex folliculorum and Demodex brevisare are parasitic mites that particularly favour the hair follicles of eyebrows and eyelashes and measure a mere fraction of a millimeter long. They crawl about your face in the dark to mate and then crawl into the pores to lay their eggs and die. Healthy adults have around one or two mites per square centimetre of facial skin, though people with the condition rosacea can have 10 times more. Demodex does not have an anus and therefore cannot get rid of its faeces. Instead, their abdomen gets bigger and bigger, and when the mite dies it decomposes and releases its faeces all at once into the pore.