Black marks on the back may be caused by melanosis, post-inflammatory hyperpigmentation, etc., which can be treated by causative therapy and medication. 1. Melanosis: black marks on the back may be melanosis, patients with melanosis should avoid contact with suspected allergenic substances, take measures to avoid light and pay attention to sun protection. 2. Post-inflammatory hyperpigmentation: black marks on the back may also be post-inflammatory hyperpigmentation, which can be treated with medications that can be taken orally as vitamin drugs, such as vitamin A, vitamin C, etc., which are used to change the skin nutrition. You can use topical decolorizing agents such as 3% to 5% hydroquinone cream topical medication, but should avoid excessive application of side effects that lead to uneven fading. Black marks on the back, it is recommended to go to the hospital in time, under the guidance of the doctor to carry out active treatment, do not take medication without authorization to avoid adverse reactions.