Human olfactory psychophysics

This is a mainstream research paper about the sense of smell and is probably the current viewpoint of the mainstream on the olfactory system. It mentions concepts such as 'specific anosmia', 'threshold', and 'adaptation'. 'Specific anosmia' is the genetic inability to smell specific smells. Fecal body odor sufferers (or other bowel smells or other odd smells) often say they cannot smell themselves. This also seems to be the general rule for people with external body odor. However, those with fecal body odor can smell feces odor from other sources (not through human skin, it seems), so specific anosmia doesn't seem to be the reason. The same seems true for trimethylaminuria and probably other metabolic body odors, although Dr John Cashman reckons perhaps 8% cannot smell trimethylamine, although it's not known if he means only from humans or from any source. for example, most people seem to be able to smell fish. Another theory for this is 'adaptation' and desensitivity to the smell. This seems more likely than specific anosmia, however, perhaps sufferers have been in situations where a group of strangers complain of a smell but one stranger says they can't smell anything (for instance in school). Adaptation and desensitivity do not seem to account for this. At the moment it is a mystery. the most likely guess is that there is some genetic aspect, as of yet unknown.

That aside, the article is seemingly the 'latest' (2004) in olfactory perception and worth a read

Human olfactory psychophysics
Andreas Kellera and Leslie B. Vosshall 2004