Dark skin has higher amounts of pigment than lighter skin. Sunlight triggers the body to make more melanin to help protect the skin from the burning rays. This causes the development of a suntan. Birthmarks, freckles, and liver spots are examples of other dark skin marks that are related to melanin levels.
Many factors increase the amount of pigment that can darken skin.
Skin damage from burning or freezing such as medical treatments with liquid nitrogen or chemical peels. Changes in hormone levels due to pregnancy, an over-active thyroid, or taking birth control pills. Injections of metals that contain pigment, as in gold shots that are given for arthritis treatment. Diseases such as Addison's disease, diabetes, and anemia. Exposure to ultraviolet light or sunlight can be harmful.