The compelling challenge of exploration has, with the advent of space probes, been extended to include much closer investigation of a variety of distant planets and their potential to support life. As spaceships reveal more and more surface environments that are barren and hostile to human habitation, like that of the moon, the enormity of the search for planets suitable for colonization is emphasized.

There are, however, equally demanding and exciting investigative challenges, though requiring different technical skills, if the telescope is exchanged for the microscope. We need look no further than ourselves to find micro-worlds ripe for exploration; each of us provides a surface that supports an interactive microbial population, the location and composition of which is dependent upon the structure and metabolism of the layers that compose our skin.

Microorganisms float unseen in the air around us, often on ‘flying saucers’ of keratin a few microns in diameter, which, as we shall see later, are derived from the surfaces of different mammals. Some of these airborne microorganisms, for genetic survival, need to colonize the skin of other individual hosts of the same or different species. However, although mammalian skin surfaces are very large in comparison to those of the microbial ‘spacecrafts’, they are, in relative terms, distant and there are abundant alternative hostile surfaces, such as the soil, roads and pavements.