| In this reference, 'odor' refers to bad-smelling substances specificly,
as opposed to substances that can be smelled in general.
Most of the chemicals of human odors are simple and biologically very common.
However, specificly studying the chemicals of human odor pertains specificly to ourselves, and is thus
more applicable.
Bad-smelling odors that are produced by human skin; particular parts of human skin such as the
armpits (due to apocrine glands), feet, and genitals; the back of
the interior of the mouth (as in halitosis); and in human waste fluids are produced mostly by
the action of bacteria on dead cells, mostly on the protein of said cells, or on other proteins. Dead skin cells consist almost exclusively of keratinocytes, which are the main cells of the epidermis. As keratinocytes age, they migrate from the base of the epidermis where they are
produced, to the surface, and during that time they accumulate the protein keratin.
Most of the human odor chemicals are metabolic break-down products of
amino acids. The following are the main bad-smelling human odor chemicals, their metabolic precursors (which are written before them), their
smell, and their bodily locality if specific:
saccharides and lipids --> acetic acid (the sour-smelling odor chemical of vinegar; acetic
acid is only produced by anaerobic bacteria)
tryptophan --> indole, skatole (odors of feces)
cysteine and methionine --> methanethiol aka methyl mercaptan (an odor of feces, also a distinctive sulfur-smelling odor of feet that is produced by brevibacteria, especially between the toes), to a lesser extent
hydrogen sulfide (the odor chemical of rotten eggs) and ethanethiol
(the odor chemical of skunk spray)
arginine --> putrescine (odor is putrid, a smell of rotting meat)
lysine --> cadaverine (odor is putrid, a smell of rotting meat)
proline --> pyrroline (odor is sickly-sweet and fish-like; occurs especially in sperm and rotten dried saliva)
leucine --> methylbutyric acid aka isovaleric acid (the odor chemical of foot odor; leucine is converted into
3-methylbutyric acid via a complex catabolic pathway that begins with ketoisocaproic acid)
alanine --> propanoic acid aka propionic acid (odor of sour milk and cheese)
niacin --> pyridine (odor is sour, putrid, and fish-like; produced especially by the vagina)
choline --> trimethylamine (the odor chemical of salt-water fish; only produced in
a substantial amount in people with fish odor syndrome)
dietary cellulose --> methane (the main odor of flatus aka farts; cellulose is converted to methane only by anaerobic bacteria) | 
