Pigmentation disorders: hyperpigmentation and hypopigmentation.

Pigmentation disorders include a large number of heterogeneous conditions that are usually characterized by altered melanocyte density, melanin concentration, or both, and result in altered pigmentation of the skin. Some of these disorders are extremely common (melasma, vitiligo), whereas others are rare. In this contribution, we review the most common pigmentation disorders that appear on the face. These lesions, even though mostly asymptomatic, have a great impact on a patient's quality of life.