Key takeaway
Felinine is cat urine's secret weapon — it slowly degrades into sulfur odorants, making the smell worse over time.
Cat urine has a chemical signature no other pet produces: felinine. This sulfur-containing amino acid is found almost exclusively in cat urine, and it is the reason cat urine gets worse with age — it slowly degrades into the sulfur compounds that produce the sharpest odor in the pet world.
What felinine is
Felinine (from felis, cat) is an amino acid containing sulfur — found in the urine of domestic cats and some wild felids, at levels far higher in males than females. It is a cat-specific compound; dog urine and most other animals do not produce it.
It is thought to be a precursor to a pheromone — a chemical signal for other cats.
Felinine is essentially a time-release odor capsule — it is mild when deposited and converts to strong sulfur odorants as it ages.
How it becomes the smell
Felinine itself is not the worst part — it degrades. Over time, it breaks down into sulfur compounds, most importantly 3-mercapto-3-methylbutanol (MMB) — a mercaptan-class molecule that produces the characteristic sharp, pungent tomcat odor.
The conversion happens after deposition — which is why cat urine smells worse days later than fresh.
MMB: the signature molecule
MMB is the molecule that says “cat” — a sulfur compound detectable at extremely low concentrations with the unmistakable tomcat character. It is produced by felinine breakdown, so it accumulates in aging urine rather than being present initially.
The delayed production is what makes cat urine a time-release odor problem.
Why males produce more
Felinine levels are much higher in intact males — it is linked to testosterone and territorial signaling. Tomcat urine is the extreme case: maximum felinine, maximum MMB production, maximum smell.
Neutering reduces felinine significantly — one reason neutered cat urine is less severe.
The marking version
Spray marking is concentrated felinine delivery — the marking urine is richer in signaling compounds than voided urine. A spray mark is a felinine deposit designed to signal; its smell is correspondingly intense.
The treatment implication
Felinine chemistry means cat urine needs the full treatment — the felinine keeps converting after cleaning if the residue remains. Removing the residue stops the conversion; leaving residue means continued MMB production.
This is why cat urine is the hardest pet urine to remediate — the chemistry keeps producing.
Where PawFresh fits
PawFresh’s enzymatic treatment removes the residue — stopping the felinine-to-MMB conversion at the source.
Sources & further reading
- Felinine chemistry and cat urine research general-science
Frequently asked questions
Why does cat urine smell worse over time?
Felinine — it degrades into sulfur compounds (MMB) after deposition, so the sharpest odorants accumulate in aged cat urine.
What is the tomcat smell?
MMB — a sulfur compound produced by felinine breakdown. It is detectable at trace levels and produces the characteristic sharp cat odor.
Does neutering reduce cat urine smell?
Yes — intact males produce the most felinine. Neutering significantly reduces it and the marking behavior.
Why is cat urine harder to clean?
The chemistry keeps producing — residual felinine keeps converting to sulfur odorants if the deposit remains.