Bad breath is judged by the following specific methods: 1, sensory perception test method, that is, the nasal breathing method. Need special testers to smell, but may testers have subjectivity. In addition, often smell odor, do not feel good, so this method is now used less; 2, chemical detection method, you can detect the level of sulfide exhaled gas, sulfide detector, but in ordinary life is not very convenient to use, so the recommended sensory breathing method, that is, to find friends and relatives smell there is no smell; 3, a relatively simple self-test method is the mouth and nose breathing method, that is, the mouth and nose covered, blow a breath, about blowing 10 seconds, and then smell whether there is no smell; 4, wear a mask, exhale the gas will basically be partly retained in the mask inside, then you can also smell the breath heavy; 5, saliva check method, that is, wash your hands clean, saliva coated in their hands, and so 10 seconds, dry smell there is no odor, which can also determine whether the breath is heavy.