The inability of a person to sense his own breath results in a situation called the “bad breath paradox” (Scott Harper, personal communication). According to this paradox, most of the people suffering from breath odors are unaware of their condition, whereas many others that do not have any breath odor worry excessively that they do. For example, in a study of 88 subjects attending a routine health check up, 19 thought that they had bad breath, but this was not confirmed by the odor judge. Conversely, nine had breath odor (as determined by the odor judge) but were not aware of it (Rosenberg et al. 2007). In another study conducted in Japan (Iwakura et al. 1994), 80% of the patients who visited the clinic claimed to be self-aware of their condition, while only 24% had actual malodor.

Some researchers attributed the inability to sense one’s own breath to olfactory accommodation or adaptation (Spouge 1964), i.e., continuous exposure to an odor stimuli resulting in specific desensitization of the olfactory system to that odorant. However, research indicates that this may not be the case, since subjects were able to sense the malodor of their saliva (Greenstein et al. 1997; Rosenberg et al. 1995) even though this malodor ostensibly comprises many of the same odorants. Therefore, it seems that the explanation for this phenomenon is much simpler. Since the malodor components are extremely volatile from the time the person exhales them, until he inhales again, their concentration drops below their detection threshold. That may be why people cannot detect their own odor while the people facing them can.

Most researchers found no correlations between self-reported breath odor ratings and breath odor objective clinical measurements as carried out by the trained odor judge (Bornstein et al. 2009; Rosenberg et al. 1995) and therefore concluded that self-reported breath odor is an unreliable parameter. One study, on the other hand, did conclude that “self-estimation of bad breath correlated well with the presence of oral malodor” (Romano et al. 2010). However, a critical review of the results of this study shows no correlation between the self-assessment and the odor judge ratings or other clinical parameters. Despite these facts, many studies still erroneously rely on self-reported breath odors, usually by means of a questionnaire as an objective parameter in breath odor investigations (for examples, see Chap. 6).

It seems that the physical inability to detect one’s breath odor is not the only limitation in self-assessment of breath odors. Research showed that even when given a sample of their odor (e.g., tongue coating sample), subjects lacked the ability to objectively rate and score the odor. It seems that there are psychological factors that color our objectivity about our own body traits, including smells. For example, in 1995, a study was reported on ­self-assessment of bad breath involving 52 subjects, 43 of whom were concerned that they did have bad breath (Rosenberg et al. 1995