The causes of many small rashes on the back of adult hands include scabies, eczema, contact dermatitis, acute urticaria, etc. The treatments are mainly medications and so on. 1. Scabies: Because the back of adult hand is infected by scabies, these scabies can damage the skin and lead to the appearance of rashes, at this time you can give 4% dilute hydrochloric acid solution coated to kill scabies treatment. 2. Eczema: because of a variety of factors triggering large-scale inflammation of the skin, at this time can appear on the back of the hands of adults with a lot of small rashes phenomenon. Hydrocortisone butyrate ointment can be used externally, if the symptoms are more serious can also be combined with oral cetirizine and other antihistamines for treatment. 3. Contact dermatitis: When the skin comes into contact with certain irritating substances, these substances can irritate the skin and lead to a rash. It can be treated with topical glucocorticosteroid drugs such as dianabed ointment under doctor’s guidance. 4. Acute urticaria: As the human body comes into contact with allergens, triggering an allergic reaction in the skin, antihistamines such as diclofenac tartaridine can be given to treat the condition. Finally, the phenomenon of many small rashes on the back of the hands of adults, please consult a doctor in a timely manner, after the cause of the disease is clear symptomatic treatment, the drug should follow the doctor’s instructions.