House smells like cat pee and you can't find it
Last reviewed · Not medical advice
The usual answer is old urine you can't see: from your cat, a previous owner's pet, or mice. Dried urine soaks into carpet pad and subfloor and re-releases its smell whenever humidity rises, which is why it seems to come and go. A UV flashlight in a dark room finds most of it. If there's no pet history, check for mice and for boxwood shrubs near open windows. One look-alike matters for safety: an overheating outlet, switch, or light fixture can give off a urine-like or fishy smell. If the smell is near anything electrical, check that first.
Most likely causes
Ranked for this situation. Open any cause for checks and fixes.
- 1
Old pet urine in carpet, pad, or subfloor
most commonIncludes previous owners' or tenants' pets. Urine in the pad or subfloor can outlast the pet by years.
Points to this:- Ammonia or cat-pee smell that gets worse on humid days or after carpet cleaning
- Previous owners or tenants had pets
Check it, fix it, who to call
Safe checks- In a dark room, scan the floor and wall bases with a UV (black) light. Dried urine often fluoresces.
- Smell close to the floor along baseboards, corners, and under furniture.
Fix- Treat with an enzyme cleaner, applied deeply enough to reach the pad.
- Replace saturated pad.
- Seal stained subfloor with an odor-blocking primer before new flooring.
DIY stops here: Saturated subfloor or tack strips mean pulling the carpet — a flooring contractor job for most people.
Who fixes it: Flooring contractor
More on this - 2
Mice or rats
commonWithin daysThe top suspect in homes with no pet history, especially in kitchens, garages, and closets.
Points to this:- Droppings in cabinets, drawers, or behind the stove or fridge
- Scratching at night; chewed packaging
Check it, fix it, who to call
Safe checks- Inspect under sinks, behind appliances, and in pantry corners with a flashlight.
- Don't sweep or vacuum droppings dry — wet them with disinfectant first and wear gloves.
Fix- Trap the mice or rats and seal entry gaps.
- Clean contaminated areas following public-health cleanup guidance.
DIY stops here: Ongoing activity, nests in walls or attic, or rats: call pest control.
Who fixes it: Pest control
More on this - 3
Overheating outlet, switch, fixture, or wiring
less commonSame dayRare as a cause of 'cat pee' smell, but the one you can't afford to miss.
Points to this:- Smell near an outlet, switch, light fixture, power strip, or the panel
- Cover plate warm to the touch, discolored, or scorched
- Lights flicker, breakers trip, or you hear buzzing
Check it, fix it, who to call
Safe checks- Smoke, sparks, or visible scorching: leave and call 911.
- Otherwise, carefully feel cover plates with the back of your hand — don't open anything.
- Unplug what's on a suspect outlet, and switch off its breaker if the panel is safe to reach.
Fix- An electrician replaces failed devices and corrects loose or overloaded wiring.
DIY stops here: Beyond switching off the breaker, nothing — warm or scorched electrical parts are electrician work, today.
Who fixes it: Licensed electrician
More on this - 4
Carpet or pad that got wet
less commonWithin daysDamp carpet pad smells sour and can reactivate old urine in it.
Points to this:- Smell strongest at floor level in one area
- Worse on humid days or after carpet cleaning
Check it, fix it, who to call
Safe checks- Press a dry paper towel hard into the carpet — dampness shows up.
- Lift a corner at the tack strip and check the pad and subfloor.
Fix- Dry the area fully with fans and a dehumidifier.
- Replace pad that stayed wet more than a day or two, or that is stained.
DIY stops here: Large areas or any sewage-contaminated carpet go to a restoration company.
Who fixes it: Water damage / restoration company
More on this - 5
Boxwood shrubs near the house
less commonIf the smell comes in through windows on one side of the house and is seasonal.
Points to this:- Smell is stronger outdoors near the hedges
- Seasonal, and worse with windows open
Check it, fix it, who to call
Safe checks- Close the windows on that side for a day and see if it stops; sniff the shrubs directly.
Fix- Keep windows on that side closed in peak season, or replace the shrubs.
DIY stops here: None.
Who fixes it: You (DIY)
More on this
How we rank causes: by how often each one explains this smell in ordinary homes, according to plumbing, HVAC, electrical, and building-science guidance, adjusted for the context on this page. The labels are judgments, not measured statistics. Anything dangerous that can't be ruled out (gas, fire, electrical) is covered in the safety box at the top of the page, whatever its rank.
Which one is it?
| Clue | Likely source | Next step |
|---|---|---|
| Worse on humid days or after carpet cleaning | Old urine in carpet pad or subfloor | UV light hunt |
| You moved in recently; previous owners had pets | Previous pet urine | UV light along walls and corners |
| Droppings, chewed packaging, scratching at night | Mice or rats | Pest control |
| Near an outlet, switch, or light; flicker or buzzing | Overheating electrical part | Breaker off, electrician |
| Stronger outside, near hedges, with windows open | Boxwood shrubs | Close those windows for a day |
| Sharp ammonia near the litter box only | Litter box itself | Clean and replace the litter |
Narrow it down
Answer in order. Stop at the first yes.
- 1Is the smell near an outlet, switch, light fixture, or power strip — or do lights flicker or buzz?Yes → Treat it as electrical: breaker off, electrician today. Go thereNo → Keep going.
- 2Has any cat or dog lived in the home, now or before you?Yes → Do the UV hunt below; it finds most old urine.No → Look for mice first: droppings under sinks and behind appliances.
- 3Is it worse on humid days?Yes → That's typical of urine salts in the pad or subfloor rehydrating.No → Keep going.
- 4Is it strongest at windows on one side, and seasonal?Yes → Check for boxwood shrubs outside those windows.
Safe checks you can do yourself
In the order that finds the source fastest.
- 1
Run a UV flashlight hunt after dark
Turn off the lights and wait a minute for your eyes to adjust. Sweep a UV (black light) flashlight slowly across the floor, along baseboards, room corners, door frames, and the lower part of walls and furniture. Dried urine often shows up as a dull yellow-green glow. Mark each spot with painter's tape. Other things glow too, so smell-check each one up close.
- 2
Smell low
Get your nose near the floor along walls, in closets, under beds, and behind furniture. Cats favor corners and vertical surfaces; floor-level smell is much stronger than standing height.
- 3
Look for mice
With a flashlight, check under sinks, behind the stove and fridge, pantry corners, and drawers. Rice-sized droppings or chewed packaging confirm it. Don't sweep droppings dry — wet them with disinfectant first and wear gloves.
- 4
Check outlets and fixtures by touch
With the back of your hand, feel cover plates and dimmer switches in the smelly area. Warm, discolored, or crackling means the safety steps above — don't open anything.
- 5
Test the windows
If the smell seems to come and go with fresh air, close the windows on one side for a day and see whether it stops.
Getting rid of cat urine smell once you've found it
Regular cleaners and odor sprays mostly don't work on urine. The smell comes back because the residue is still in the material. Enzyme cleaners made for pet urine break that residue down — but only where they reach. Soak the spot generously so it reaches as deep as the urine did, keep it damp for the time on the label, then let it air-dry fully.
Carpet is the hard case. If the UV light shows a large stain, or the smell comes back after enzyme treatment, the pad underneath is saturated. Pull back the carpet: replace the stained pad, treat the subfloor with enzyme cleaner, and once it's dry, seal it with an odor-blocking primer before the pad goes back down.
Avoid steam cleaning or heat on urine spots before treating them. Heat can set the smell into the fibers.
When DIY stops
- Any sign of electrical overheating: warmth, discoloration, flicker, buzzing, or a tripping breaker.
- Urine soaked through to the subfloor or into the tack strips across a large area.
- Ongoing mouse or rat activity, nests in walls or the attic, or any sign of rats.
Who to call
- Licensed electrician
The smell is near outlets, switches, lights, or the panel.
Outlets, switches, wiring, panels, and light fixtures.
- Pest control
You find droppings or hear scratching.
Finds and removes mice and rats, and seals entry points.
- Flooring contractor
The pad or subfloor is saturated and needs pulling, sealing, or replacing.
Pulls carpet and pad, seals or replaces contaminated subfloor.
Answer a few questions about where and when you smell it. You'll get the causes ranked for your situation.
Frequently asked questions
Why does my house smell like cat pee when I don't have a cat?
The most common reasons are a previous owner's pet (urine in the carpet pad or subfloor), mice, or boxwood shrubs near open windows. Less often, it's an overheating electrical part — check outlets and fixtures near the smell.
What does an ammonia smell in the house mean?
Most often old urine, from pets or rodents, or an overdue litter box. Ammonia-based cleaners also leave the smell. If it's sharp and near something electrical, treat it as possible overheating.
Why does the cat pee smell get worse when it's humid?
Dried urine leaves salts that pull moisture from the air. When they get damp, they release their smell again. That's why a stain can seem gone for months, then come back on a rainy week.
Can mold smell like cat pee?
Some people describe certain musty smells as urine-like, but mold usually reads as earthy or damp. If UV finds nothing and there are no mice, check for moisture too.