The propionibacterium acnes (PAC) which causes the inflammatory reaction of skin, is a kind of anaerobic bacteria which produces porphyrin(a sort of photosensitive substance) during metabolism. The special spectrum of GSD IPL penetrates deep into skin tissues and is absorbed by porphyrin, stimulates porphyrin to release monomorphism oxyanion which kills propionibacterium acnes effectively, as a result of which, clears acne.