Inflammation of certain areas, Addison's disease, hemochromatosis, tinea versicolor, pityriasis alba and vitiligo can all cause the skin to turn different colors. These diseases are often the result of different factors, but present themselves on patches of skin by causing them to become darker or lighter than the rest of the skin.
Skin has special cells inside of it called melanocytes. These cells are what gives skin its coloring. When the cells that are in the skin are affected by disease or even trauma, they will not produce the important melanin that is necessary for pigmentation of the skin; they may also produce too much melanin. When people have discolored skin, whether it is darker or lighter, they are generally not suffering from a serious medical condition.
After visiting a physician to rule out any type of serious medical condition, patients can focus simply on the treatment of the discolored skin. There are special over-the-counter creams that will be able to lighten areas of darkened skin. Patients can also use inexpensive cosmetics to help reduce the appearance of the discoloration while deciding on a course of action for the treatment of the areas of skin that are darker or lighter.