Aristotle’s “extremity of a thing” (Metaphysics, V), and Euclid’s “extremity of anything” (Elements, I) have been important to my work on the difference between air and water, and to development of a social theory of microbiomic sociality—my angry swipe at multispecies ethnography. In this chapter, I use Steven Connor’s (2002) notion that the skin is not part of the body to examine anthropology’s capacity to deliver a conceptualisation of the skin critical to human survival.