Red patches on the back of hands may be caused by allergy, frostbite, nevus erythematosus and other diseases. 1. Allergy: red patches on the back of the hand may be caused by allergy, the patient will also have itching, before the onset of more contact with pollen, animal hair and other allergy-prone substances, should avoid re-exposure to allergens, can be treated with antihistamine drugs such as loratadine. 2. Frostbite: red patches on the back of the hands may also be caused by frostbite, which occurs in winter, itching and pain, and such people should pay attention to keep warm. 3. nevus erythematosus: red patches on the back of the hand may also be caused by nevus erythematosus, which is a congenital capillary malformation, also known as red birthmark, the border is clear, not higher than the skin, can be eliminated through surgery or laser. It is recommended that the patient should consult a doctor in time to clarify the cause of the disease and then carry out the corresponding treatment, and the above medicines and treatments should be carried out under the guidance of a doctor.