The hands are red, swollen and itchy for no reason, and may be caused by contact dermatitis, salpingitis, insect bite dermatitis and other diseases, usually using medication. 1. Contact dermatitis: when the hands come into contact with certain external substances, such as gloves, detergent, etc., may trigger contact dermatitis, manifested as erythema and edema on the skin surface, accompanied by intense itching. Local topical glucocorticoid ointment, such as mometasone furoate cream, etc., if the itching is serious, you can also take antihistamines, such as loratadine tablets. 2. Dengue: Dengue is mostly caused by B hemolytic streptococcus infection, manifested as skin edema, erythema, blisters, etc., may be accompanied by pain, itching and other symptoms. Oral penicillin treatment, if penicillin allergy, oral macrolides, such as roxithromycin, etc., can be used externally with furacilin solution wet compresses, and topical antibiotic ointment, such as mupirocin ointment. 3. Insect bite dermatitis: occurs in summer, due to mosquito bites. Often manifested in the bite site redness, swelling, doughnut-like erythema, papules and other manifestations, accompanied by itching. At this time, you can use glycerine lotion or hydrocortisone butyrate cream and other drugs. The above drugs should not be used privately to avoid adverse reactions, it is recommended to use under the guidance of a doctor. The redness, swelling and itching of the hands for no reason may also have other causes, you should go to the hospital in time, to clarify the cause of the disease to give targeted treatment.