Sore arms on rainy days are mainly caused by rheumatoid arthritis, fasciitis, environmental factors and other reasons. 1. Rheumatoid arthritis: mainly due to streptococcal infection, cold weather, humid air and other reasons can induce symptoms. It can be manifested as wandering polyarthritis. Due to the stimulation of inflammation, there can be soreness and pain, and the common sore parts are arms, feet, ankles, shoulders, and so on. 2. Fasciitis: may be due to the body by the cold, damp climate, chronic strain, trauma and other causes of inflammation, when the arm fasciitis, which can appear in the rainy day arm pain phenomenon. 3. Environmental factors: on rainy days, the air is humid and the temperature is cold. This may stimulate the muscles of the arm, resulting in soreness. It is recommended that patients with arm pain on rainy days go to the hospital in time and follow the doctor’s instructions for treatment to avoid delaying their condition.