Moles appearing on the chest are usually pigmented nevi. The cause of sudden growth of many moles on the chest is not clear, and may be related to congenital heredity, hormone level changes, ultraviolet radiation and so on. Pigmented nevus is a common benign skin tumor, which may be related to congenital genetic factors, developmental defects, gene mutation and so on. In some patients, the sudden growth of many moles on the chest is related to the change of hormone level, ultraviolet radiation, trauma, medication, immunosuppression and other factors. In addition to the chest, pigmented nevi can also occur on the head, face, limbs and other parts of the body. In most cases, pigmented nevi do not affect health and do not need treatment, and if necessary, they can be treated with surgical excision or laser treatment. In daily life, patients need to strengthen the local skin care, avoid foreign body friction stimulation. When going out, do a good job of sun protection, avoid direct sunlight exposure to the skin. If it is caused by medication, the amount of medication can be adjusted or replaced with other medication as prescribed by the doctor. It is recommended that people who have many moles on their chest should follow the doctor’s instructions, and should not use drugs or prescriptions on their own in order to prevent skin damage and infection.