Adapted From: https://www.meboblog.com/2008/04/chemical-composition-of-odors-chemical.html

Posted on Friday, April 11, 2008

Formatted, and expanded version of Maria's notes. I standardized names, corrected spellings, grouped similar compounds, and added missing or commonly associated origins where appropriate.

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Chemical Composition of Odors

Format: Chemical → Characteristic Odor → Likely Origin / Source

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 / Additions That Fit This List

• 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