From The National Geographic:
High magnification reveals a host of bacteria underneath a human toenail. A new analysis has shown that the billions of bacteria that inhabit human skin are not only highly diverse but also change their composition over time. Understanding how and why the microbes change could lead to better treatments from chronic skin disorders such as psoriasis and eczema. When we change our soap [or] shampoo [or] laundry detergent, when we change whether we’re wearing a cotton shirt or a wool shirt, all of these are going to have an effect on our skin flora.