Marla Ahlgrimm reports that one of the most common reasons for loss of pigmentation is vitiligo, especially in people of African or Southern European descent. Vitiligo often start out as a slight bleaching of the skin and gradually becomes more noticeable with age. While not harmful, vitiligo may indicate other issues, such as a thyroid disorder.
Melasma, the mask of pregnancy, is the opposite of vitiligo. When a woman is pregnant, her skin cells sometimes produce more pigment, which can result in a brown to gray-brown tint on the face. 90% of melasma cases are in women and it is widely believed to be associated with hormones, says Marla Ahlgrimm.