Darkened, Tanned Skin
Primary reason for dark pigmented skin is due to exposure to the sun. The ultraviolet rays cause an increase in melanin, thereby leading to a darker appearance. it is primarily seen on sun exposed areas like face, neck, hands etc. It is also environmental in nature such that in increases in places of higher altitude and beaches where there is a higher exposure to uv rays. Outdoor activities like swimming also tend to affect the same.
Sometimes tan disappears on it's own over few days in cases of sun exposure for short duration. But in cases of continuous and prolonged sun exposure tanning keeps on increasing and is near permanent in nature.
Primary reason for dark pigmented skin is