Small red spots on the skin turn black like moles may be caused by other reasons such as purpura, hyperpigmentation, pigmented nevi and so on. 1. Allergic purpura: The cause of allergic purpura is still unclear, and it is considered to be related to infection, heredity, drug factors and other reasons. Patients will have purple-red papules in the early stage, with the development of the disease will be changed to dark purple papules, and eventually the papules will be brown, and subside, so the patients will have a small red spots on the skin and then turn black like a mole performance. 2. Hyperpigmentation: If local inflammation occurs, after the inflammation recovers, it will stimulate the skin to produce hyperpigmentation, so the skin will appear to be black like a mole after a red spot. 3. pigmented nevus: if the local first appeared small red spots, and then turned black like a mole, there may be no clear correlation between the two. The previous appearance of dermatitis eczema and other diseases, skin lesions subside in the original rash site appeared in the pigmented nevus. It is recommended that small red dots on the skin turn black like a nevus need to consult a doctor in a timely manner, the doctor will be clear after the cause of the disease to choose the appropriate measures for treatment.