Possible causes of subcutaneous bleeding spots on one arm in infants include allergic purpura, immune thrombocytopenia, and hemophilia. Treatment is mainly drug therapy. 1. Anaphylactic purpura: mainly manifested as skin petechiae and purpura, mostly confined to the limbs and buttocks. At present, there is no specific treatment, mainly to take support and symptomatic treatment, commonly used therapeutic drugs, including aspirin, cetirizine hydrochloride drops, methylprednisolone and so on. 2. Immune thrombocytopenia: the main manifestation is skin or mucous membrane bleeding spots, petechiae or ecchymosis, which can be treated with glucocorticosteroids (e.g., methylprednisolone) and static injection of human immunoglobulin as prescribed by the doctor. 3. Hemophilia: a group of hereditary coagulation dysfunction bleeding disorder, due to the subcutaneous tissue, oral cavity, gingival mucosa is easy to injure, for the bleeding site. Alternative treatment is an important measure in the treatment of hemophilia, and the available preparations mainly include genetically recombinant FⅧ concentrated preparation, fresh frozen plasma, cold precipitates, and thromboplastin complex. Infants with subcutaneous bleeding spots on one arm may also be related to other causes, and it is recommended to consult a doctor in time, make a clear diagnosis under the guidance of the doctor, and carry out targeted treatment. The above drugs should be used under the guidance of a doctor.