If it is a weak laser LED red light, there will be no scar. It is because the stimulation of collagen synthesis, the influence of red light on various bioactive enzymes in tissues, the stimulation of new capillaries and the increase of immunoglobulin in the secretion of ulcer surface after irradiation are the material basis for red light to promote the healing of ulcer surface. Therefore, the ulcer site can be repaired and healed with moderate dose of red light, and the new epithelium will be covered without forming scars.