There are small red dots on the body after a while into small black dots, common causes include eczema, allergic purpura, etc., the general use of medication, physical therapy methods, such as hydrocortisone cream, laser treatment, and so on. 1. Eczema: local topical glucocorticoid ointment, such as hydrocortisone cream, halomethasone cream, etc., to be inflammation subsides, can be local topical hydroquinone cream, cumene glycoside cream ointment to reduce hyperpigmentation, but also can be used in physical therapy, such as photorejuvenation, etc., to improve the symptoms of the small black spots effectively. 2. Henochromatosis purpura: Henochromatosis purpura caused by small black spots, generally with the passage of time will gradually subside, the patient can also be applied locally arbutin cream, tretinoin cream, etc., can also be used in physical therapy methods, such as picosecond laser, etc., to accelerate the subsidence of the black spots. All of the above drugs should be used under the guidance of a professional doctor, avoid self-medication. There may be other causes for the small red dots to turn into small black dots, it is recommended to go to the hospital in a timely manner to improve the examination, to clarify the cause of the disease and then give targeted treatment.