As an aside, mites live not just in our beds but on our skin as well. I couldn't find authoritative data on face-mite populations, but here's one very rough attempt. One study took mite samples from six facial locations with cumulative surface area of 10 cm 2 (p. 444). Mite counts on normal subjects averaged individuals (Table I, p. 445). This suggests roughly 1 mite/cm 2 . I doubt the sampling sites were perfectly representative of all areas of the skin on the human head, but assume they were. Assume the human head is a sphere with radius ~10 cm. Its surface area is then 4 * pi * radius 2 = 4 * pi * 10 2 = 1256 cm 2 , which implies ~10 3 mites per face and ~10 13 mites added over all human faces. I don't know if this is about right or way off. By comparison with the bed dust-mite numbers above, it seems somewhat low, but maybe vastly more mites can live on the copious quantities of dead skin in beds than on the small amounts of dead skin and oils on people.