Adapted on 2/15/2026 from: https://www.meboblog.com/2008/04/chemical-composition-of-odors-chemical.html

Formatted, and expanded version of Maria de La Torre's post of Friday, April 11, 2008

See also old Aurametrix Notes about this. 

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Chemical Composition of Odors

Sulfur compounds

Chemical	Odor	Origin / Source
Hydrogen sulfide	Rotten eggs	Sulfur metabolism; amino acids (e.g., methionine, cysteine)
Methyl mercaptan (methanethiol)	Rotten cabbage	Sulfur-containing amino acids
Diethyl sulfide	Rotten vegetables	Sulfur compounds from protein breakdown
Methionine	Rancid butter	Sulfur amino acid metabolism

Phenolic & aromatic compounds

Chemical	Odor	Origin / Source
Phenol	Medicinal, sweet	Tyrosine metabolism
p-Cresol	Fecal	Tryptophan, tyrosine degradation
Phenylalanine	Musty / mousy	Amino acid metabolism
2-Aminoacetophenone	Musky, grape-like	Microbial metabolism
Indole + other compounds	“Wet dog” odor	Protein decomposition

Nitrogenous amines

Chemical	Odor	Origin / Source
Methylamine	Fishy, pungent	Nitrogen metabolism
Dimethylamine	Fishy	Protein degradation
Diethylamine	Pungent, ammoniacal	Nitrogen compounds
Trimethylamine	Fishy, ammoniacal	Choline metabolism
Ammonia	Sharp, pungent	Protein breakdown, urea metabolism
Dimethylglycine	Fishy	Choline metabolism
Cadaverine	Rotting corpse	Lysine decomposition

Indoles & related compounds

Chemical	Odor	Origin / Source
Indole	Fecal, mothball-like	Tryptophan breakdown
Skatole	Fecal, pungent	Tryptophan metabolism

Organic acids (short-chain & volatile)

Chemical	Odor	Origin / Source
Acetic acid	Vinegar	Fermentation; carbohydrate metabolism
Butanoic (butyric) acid	Rancid butter, sour meat	Fiber fermentation; amino acids
Caproic / capric acid	Sour, goat-like	Short-chain fatty acid metabolism
Isovaleric acid	Sweaty feet	Leucine metabolism
Methylcrotonic acid	Cat urine	Organic acid metabolism
Branched-chain amino acids	Maple syrup-like	Amino acid disorders/metabolism

Ketones & aldehydes

Chemical	Odor	Origin / Source
Acetaldehyde	Fruity, pungent	Alcohol metabolism; fermentation
Acetone	Sweet, pungent	Fat metabolism; ketosis
2-Nonanone	Fruity	Lipid metabolism

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Notes

• Many odors originate from microbial metabolism of:

  • Amino acids

  • Lipids

  • Carbohydrates

• Common biochemical sources of odor compounds

  • Protein decomposition → amines, indoles, sulfur gases

  • Fat breakdown → ketones, short-chain fatty acids

  • Fermentation → organic acids, aldehydes

• Key amino acid–odor links

  • Tryptophan → indole, skatole

  • Tyrosine → phenol, cresols

  • Lysine → cadaverine

  • Leucine → isovaleric acid

  • Methionine/cysteine → sulfur odors

MAPPING OF ODORS

Described odor	Similar Odor	Why
Rotten eggs	Fecal	Sulfur compounds (e.g., hydrogen sulfide) are common in fecal odors
Rotten cabbage	Fecal	Sulfurous, putrefaction-type smell typical of fecal decomposition
Rotten vegetables	Fecal	Putrid, decomposition odor similar to fecal notes
Rancid butter	Fatty	Classic oxidized-fat smell (butyric/related fatty acids)
“Wet dog”	Foot odor	Microbial, sweaty, slightly sour—similar to foot-associated bacteria
Medicinal	Underarm odor	Sharp, chemical, phenolic notes often linked to apocrine sweat breakdown
Cat urine	Ammonia-like	Strong ammonia/urea breakdown odor
Fruity	Underarm odor	Some underarm bacteria produce sweet/ester-like scents
Pungent	Underarm odor	Sharp, acrid body-odor character typical of armpit sweat compounds
Maple syrup	Fatty	Sweet, warm, lactone/organic-acid notes often grouped with fatty odors