Sore legs when it rains may be due to rheumatoid arthritis, muscle strain, old injuries and other causes. 1. Rheumatoid arthritis: its etiology may be related to streptococcal infection, environmental factors and other reasons. Due to the stimulation of inflammation, patients may experience soreness and pain in the legs, which can be aggravated when it rains. 2. Muscle strain: It may be caused by long-term labor, long-term weight-bearing and other causes of leg muscle strain. When it rains, the air is damp and cold, which can cause local vasoconstriction and poor blood flow can cause leg pain. 3. Scarring: If the knee joint area has been traumatized before, scarring may form in the subcutaneous tissue after the skin heals. Part of the scar tissue within the nerve fibers are sensitive to external climate change, when the knee area is cold, damp stimulation, can lead to scar tissue, as well as the contraction of the surrounding muscles, blood vessels, and then the symptoms of pain. It is recommended that patients who suffer from leg pain when it rains should go to the hospital in time to get a clear picture of the cause of the problem and then follow the doctor’s instructions to avoid delaying their condition.