If your knee hurts when you blow on the air conditioner, it may be due to the following reasons: 1. Synovitis of the knee may exist. This type of disease is often due to long-term cold in the knee joint, resulting in inflammation of the synovial membrane inside the knee joint, resulting in increased joint effusion and joint pain. This type of disease is often aggravated when the knee joint is cold again. 2. There may be osteoarthritis of the knee joint. It is more common in the elderly and is often caused by excessive wear and tear on the knee joint. In such patients, cold exposure to the knee joint, such as when blowing on the air conditioner, can induce significant pain. 3, there may be a condition of patellar chondromalacia. This type of disease is caused by the patient doing strenuous activities involving the knee joint, resulting in wear and tear of the articular cartilage around the patella. If the knee joint is blown by the air conditioner, such patients will have severe pain around the knee.4. This condition may also be caused by the presence of old injuries to the knee joint, such as old fractures, dislocations or other injuries around the knee joint, and after its recovery, it is often particularly afraid of cold, and once it is cold, it may cause pain around the knee.