Various factors contribute to halitosis, such as smoking, food smell, etc., but intraoral factors are significant. There are many niches for bacteria in oral cavity, so they are suitable for the growth of microorganism. Oral anaerobes can produce volatile sulfur compounds (VSCs) including hydrogen sulfide, methyl mercaptan, dimethyl sulfide and minor components including amines and acids, which may be associated with malodor. Hydrogen sulfide and methyl mercaptan are considered as major ingredients of VSCs responsible for halitosis. This review of literature illustrates the formation and the affiliated intraoral factors to halitosis.