The common causes of purple patches on the hands include trauma, purpura, primary immune thrombocytopenia and so on. 1. Trauma: If the patient’s hand skin is hit, bruised and other traumatic injuries, can lead to localized subcutaneous bleeding, which can be seen in the epidermis of the purple patches, usually the condition is not serious, these purple ecchymosis can be absorbed by the disappearance of the patches. 2. Anaphylactic purpura: the etiology of this disease is relatively complex, may be related to bacteria, viruses, food, drugs (such as salicylates, antibiotics, barbiturates, etc.) and other factors, can occur in the skin of the hands, usually before the onset of upper respiratory tract infection, low-grade fever, general malaise and other antecedents, then red papules, purpura, petechiae and other symptoms. 3. Primary immune thrombocytopenia: this disease is related to anti-platelet autoantibodies, T-cell abnormalities, platelet-related antigens, viral infections, etc. It manifests itself as petechiae on the distal skin of the limbs, and in severe cases, the petechiae may merge into patches or form blood blisters, and even symptoms such as fatigue may appear. It is recommended that patients, if necessary, go to the dermatology department of regular hospitals, follow the doctor’s instructions to clarify the diagnosis and timely treatment to avoid delaying the condition.