Hyperpigmentation in skin is caused by an increase in melanin, the substance in the body that is responsible for color (pigment). Certain conditions, such as decreased function of the adrenal gland), may cause a greater production of melanin and hyperpigmentation. Exposure to sunlight is a major cause of hyperpigmentaion, and will darken already hyperpigmented areas. Hyperpigmentation can also be caused by various drugs, including some antibiotics. Consult Dermatologist for further evaluation...