Melasma, a common skin problem triggered by sun exposure, appears as brown to gray-brown patches on the skin. It frequently occurs on the face, including the cheeks, bridge of the nose, forehead, chin, and above the upper lip, but also can appear on other parts of the body that are frequently exposed to the sun, such as the forearms and neck.
Vitiligo causes areas of the skin to lose color, creating patches of lighter skin. Some people develop only a few patches while others lose much more skin color. This skin disease often forms on both sides of the body, as is seen here on the knees.
Vitiligo usually affects only the skin, but it can develop anywhere that pigment exists. Patches of hair can turn white, people can lose color inside their mouths, and even an eye can lose some of its color.