I believe that our skin is the border between our inside and outside world. The inside and outside world interact with each other, through our skin surface. To be able to understand how this 'interaction' works, and which consequence it has for our skin, I look into the principle of (applied) mathematical 'flux'.
Flux(us) means flow, and is often used with the terms current and density. Flux can be seen as a transport phenomena (mass transfer and fluid dynamics). It is then defined as the rate of flow of a property per unit area [quantity]·[time]−1·[area]−1
But flux can also be represented by the surface integral of a vector field. The simplest way to think of 'surface flux' is: "how much coffee goes through a filter", where the coffee is a velocity field and the filter is the boundary of an imaginary surface. [quantity]·[time]−1
the symbol for flux: Φ
Source: https://en.wikipedia.org/wiki/Flux (derived 23-3-2016)