The dark marks left after acne usually take about 6-9 months to heal themselves. Acne is mainly acne, which is a chronic inflammatory papule caused by a large number of anaerobic bacteria infecting the inside of the sebaceous glands of the hair follicles. During the formation of this disease, it can affect the surrounding tissues to a certain extent. After healing, the local skin may leave black traces, which are called post-inflammatory hyperpigmentation. This kind of marks usually heals itself gradually over time, but it takes a longer time to fade away, usually 6-9 months, because this process requires its own macrophages to gradually engulf the subcutaneous melanin so that the color returns to normal. The black marks left after acne, you can go to the dermatology, laser cosmetology, under the guidance of the doctor to try to use some medical-type laser to assist in the treatment, which will help the black marks fade.