Patients with red patches on the skin of the knee can be caused by a variety of causes and conditions. For example, with rheumatic knee arthritis, due to rheumatism invades the knee joint will be formed in the local skin rheumatic nodules, the patient will have red patches of manifestations, in the cold after the nodule phenomenon will gradually aggravate. This phenomenon will be gradually relieved after hot compresses or anti-rheumatic treatment. If the patient has localized contact dermatitis or allergic reaction in the knee joint, this clinical manifestation will also appear in appearance, and will gradually disappear after giving the correct symptomatic treatment. Therefore, patients with this clinical manifestation need to consult the doctor in time, and the doctor can take the right treatment to relieve.