There are several reasons for lingering pet odors in a home. I will list a few reasons (There are many.) that this happens and a few ways to combat these issues.

1. Pet urine has penetrated both the carpet and the padding.
When pets urinate on carpet, they often leave small , yellow to orange, circular 2” to 6” stains on the surface of the carpet. These stains appear small on the carpet surface, but are actually a bit larger when you take a look underneath the carpet. When urine penetrates through carpet padding, the padding acts as a sponge absorbing urine. If a pet urinates in the same spot more than once or if a large pet urinates, the urine generally penetrates through the carpet and padding on through to the sub-floor. When this occurs, it is often necessary to seal the subfloor to completely remove the pet contamination and all associated odors. Sealing the sub-floor, in conjunction with the application of enzymatic solutions to carpet and padding, is the only way to guarantee the complete removal of pet contamination. It is VERY possible to have a heavy pet odor linger even after replacing all contaminated carpet and padding from a residence. If left untreated in the sub-floor, urine can shift phases from a liquid to a crystalline form. When dry, the urine will be almost odorless. However, if you add moisture to the equation, the urine emits a heavy, pungent ammonia scent that would drive any homeowner crazy. If pet contamination goes untreated, it may not emit much of an odor on a cold, dry, wintry day. However, on a hot, humid summer day, the odor would be quite unbearable.

2. The pet has contaminated an area that you may not have located.
As much as we’d love to think our pets are perfect little angels, some of them are quite the opposite. Who knows what goes on in the minds of our furry friends. We can train them that going on the living room carpet is a bad idea. But sometimes, the idea gets misconstrued and they’ll find the furthest corner of the house where you rarely go and soil away. One of my cats liked to go behind the washing machine of all places.

3. The pet odor may have originated from an external source.
If a pet has contaminated an area close to a door, vent or window, it is possible for the odor to waft indoors.

4. The previous owner or inhabitant of the dwelling may have had an animal.
It is quite possible that someone may have address surface pet contamination, while omitting all subsurface issues in the home.  In homes where many odor masking agents are used, such as plug-in air fresheners, carpet fresheners, aerosols, candles and other fragrance emitting agents, odors may not manifest until weeks after the home has been vacated.