In previous posts we have learned that the top skin layer consists of 5 "floors" and the 1st is occupied by newborn cells and their mums.
But it also have guards who`s job is to protect skin from Sun: as soon as we get out in the sunshine guards become active and in order to protect skin they start throwing black umbrellas up to the surface (see the carousel).
Due to a large amount of umbrellas being released, our skin shade becomes darker (tan).
However places, which are covered in clothing do not chage in colour: if there is no sun and danger, guards are asleep and do not release a single umbrella.
If we spend too much time under direct Sun without protection, some guards may go crazy and start throwing enormous amounts of black umbrellas. Due to a high concentration of umbrellas in this spot- pigmentation may appear.
Umbrellas: pigment melanin;
5 floor building: Epidermis (top skin layer);
1st floor of Epidermis: basal layer;
Inhabitants of the 1st floor: keratinocytes.