Vitiligo
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.
Pregnancy
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.