Why the smell keeps coming back
Pet urine is made of several compounds, and most of them rinse away easily. The problem is the uric acid. As urine dries it leaves behind uric acid crystals that are not water-soluble — soap, vinegar and even steam don't dissolve them. They settle deep into the carpet fibres, the backing, and the underpad beneath.
Those crystals are odourless when dry, but the moment the air gets humid they reactivate and release that sharp ammonia smell all over again. That's why a spot you "cleaned" weeks ago suddenly stinks on a rainy day. Until the uric acid itself is broken down, the odour will always come back. That single fact is the key to everything below.
What you'll need
- Clean white cloths or paper towels
- An enzymatic pet-odour cleaner (the non-negotiable item)
- A spray bottle of cool water
- Optional: baking soda, and white vinegar for fresh accidents
Step-by-step: removing fresh pet urine
Blot up everything you can
Press clean towels down hard to soak up as much urine as possible. Stand on a thick pad of towels if you need to. The less liquid left in the carpet, the less ends up in the underpad. Don't rub — that spreads it and frays the fibres.
Rinse lightly with cool water
Mist the area with cool water and blot again. This dilutes what's left before it dries. Use cool, never hot — heat sets the proteins.
Apply the enzyme cleaner generously
Saturate the spot so the cleaner reaches as deep as the urine did — a light surface spray won't reach crystals in the backing. The enzymes need to physically contact the uric acid to digest it.
Let it dwell, then air-dry
Leave it for the full time on the label — often several hours. Cover it with a towel to slow evaporation so the enzymes keep working, then let it air-dry completely. Resist the urge to rinse it out early.
Finish and check
Once dry, vacuum the area. If a faint smell lingers, repeat — set-in spots often need two passes. A light sprinkle of baking soda left overnight and vacuumed up helps with any residual surface odour.
Old, dried-in urine
Urine that has dried and soaked through to the backing and underpad is far harder. Re-wet the area, apply a generous amount of enzyme cleaner so it penetrates as deeply as the original accident, cover it, and give the enzymes several hours. You may need to repeat. If a pet has used the same spot repeatedly, the underpad and even the subfloor can be saturated — at that point no surface cleaner will fully fix it, and the padding may need replacing.
1. Steam cleaning first. Heat bonds the uric acid proteins to the fibres and sets the smell permanently — always enzyme-treat before any hot-water extraction. 2. Using ammonia-based cleaners. Urine contains ammonia, so ammonia cleaners can actually encourage a pet to re-mark the spot. 3. Mixing cleaners. Never combine bleach with vinegar or ammonia — it releases toxic gas (here's why).
When to call a professional
DIY handles most single accidents. Bring in a professional carpet cleaner when: the smell survives two or three proper enzyme treatments; a pet has soaked the same area repeatedly; the odour covers a large area or multiple rooms; or you're preparing a property for sale or new tenants and need it genuinely gone. Professionals can pre-treat, sub-surface extract, and assess whether the underpad is the real source — which usually costs less than buying bottle after bottle of cleaner that can't reach deep enough.
Frequently asked questions
Why does pet urine smell come back in carpet?
Dried urine leaves uric acid crystals that water, soap and steam don't dissolve. They sit deep in the fibres, backing and underpad, and reactivate whenever the air is humid — releasing the smell again. Only an enzyme cleaner that breaks down the uric acid removes it at the source.
What is the best thing to get pet urine smell out of carpet?
An enzymatic pet-odour cleaner — the enzymes digest the uric acid that causes the lingering smell. Blot first, saturate so it reaches as deep as the urine did, and let it dwell the full time. Vinegar and baking soda help with fresh surface accidents but won't remove set-in odour alone.
Does steam cleaning remove pet urine smell?
Not by itself, and the heat can make it permanent by bonding the proteins to the fibres. Enzyme-treat and dry first; only then consider hot-water extraction. For deep or repeated accidents, a professional with proper pre-treatment is safer.
How do you get old, dried pet urine smell out of carpet?
Re-wet the area, apply enzyme cleaner generously so it penetrates as deep as the urine did, cover it, and let it work for several hours. Repeat if needed. Repeated soaking may mean the underpad has to be replaced — when in doubt, get a professional assessment.
Odour won't budge? We'll get to the source.
Our carpet and upholstery cleaning uses professional pre-treatment and extraction to reach the urine deep in the backing — not just the surface. Serving homes and facilities across the GTA. $5M insured, WSIB compliant, no long-term contracts.