Want to know if you have bad breath: first, lick your arm with the middle of your tongue on a clean arm, wait 5-6 seconds after the saliva evaporates clean, and then smell the place you just licked, if there is an odor to prove that you have bad breath. Second, cover your mouth and nose with your hand, while breathing out, if the breath has an abnormal smell, it also indicates bad breath. Third, you can use dental floss to clean out the food debris in the teeth, smell the floss, food debris, if there is an odor to prove that there is bad breath in the mouth. Fourth, gently wipe the root of the tongue with a cotton swab or gauze, take out the swab or gauze to smell if there is an odor, if there is an odor indicates the presence of bad breath.