Skin colour is due to the dark pigment melanin which is produced by pigment cells in the lowest layer of the skin. There is the same number of pigment producing cells in the skin of all races but the amount of melanin produced varies. In dark-skinned people of tropical regions, there is more melanin because intensity of the ultraviolet radiation from the sun is stronger in the tropics. The extra melanin protects the skin from the harmful effects of ultraviolet radiation. In people living in the higher latitudes, the skin colour is lighter as they have less pigment. The lighter skin also helps in the production of vitamin D in the body under the low intensity of sunlight available. Other factors contributing to skin colour are the blood in the blood vessels of the skin and the natural yellowish tinge of the skin tissue.