The causes of dark spots on chest include pigmented nevus, age spots, chloasma, melanoma and so on. 1. Pigmented nevus: If it is pigmented nevus, at this time, due to the large accumulation of pigmented nevus cells, the phenomenon of black spots can appear on the chest. 2. Age spots: due to the aging of cells, pigmentation is not metabolized on the skin, so black spots are formed. 3. Melasma: when the hormone level is abnormal, it can stimulate the melanocytes to secrete melanin particles, thus forming dark spots. 4. Melanoma: due to various factors, pigment cells proliferate, thus forming black spots on the chest. Please go to the hospital in time for examination of the phenomenon of black spots on chest, and standardize the treatment under the guidance of professional doctors after diagnosis.