After wisdom tooth extraction, the cotton used to stop bleeding is usually taken off after about 30-40 minutes. Usually, after wisdom tooth extraction, there will be a wound left in the extraction wound and there will be blood oozing from the wound, so a cotton ball or cotton roll should be pressed on the wound and then bitten tightly, which can play the effect of pressure to stop the bleeding. In general, the extraction wound will form a preliminary blood clot in about 30 minutes, at which time there will be no more obvious blood oozing out, so the time for pressure to stop bleeding is about 30-40 minutes. If it is taken off too early, it may cause more local bleeding and also local hematoma, which will affect the recovery of the whole wound. If removed too late, it may stick completely with the blood clot, and when the cotton ball is removed, the blood clot will be spit out at the same time, which will cause infection in the dental wound instead. Patients should be careful not to brush their teeth or rinse their mouths for 24 hours after tooth extraction, not to lick the wound with their tongues, and not to create a more intense negative pressure environment in the mouth so as not to stimulate the wound.