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My bathroom has started smelling like cat urine. We have NO cats. I think the smell is coming from the shower drain.

What could this smell be coming from and how do I get rid of it?

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One possibility: if MDF gets wet, the formaldehyde in it can release urea, which smells just like cat urine. If you have MDF cabinets in the room, check them for water damage. – Niall C. Aug 19 '13 at 21:09
Is the shower used regularly? If not, could be that the trap has dried out and you're smelling gasses from the waste lines of your house. Try turning it on for a few minutes or dumping some water down the drain, and if that clears up the smell. – gregmac Aug 19 '13 at 21:21
Just want to throw in the obvious possibility that it is people urine that smells like cat urine. – Edwin Aug 19 '13 at 21:27

Look for leaks, the most likely culprit is a failed seal on the toilet. If the toilet rocks or moves that will damage the seal and cause leaks. Even if it was installed tight to the floor it is possible the seal (usually a wax ring) was not large enough, or was not replaced by a previous homeowner after removing the toilet. Also check if the toilet is caulked to the floor, this should never be done. It just traps leaks under the toilet where they will ruin the floor without you noticing.

Remove the toilet and inspect underneath. If the floor isn't rotten and the flange is not broken replace the wax seal and remount. Or hire a plumber to do the same.

Also even if you don't have cats the previous homeowner may have and moisture from showering is bringing out the smell. Think about where you would put a catbox and inspect and sniff carefully. It is common for cats to pee against the baseboards and the urine to seep under the flooring. If water gets on the floor it will bring up the smell.

In one case I had to tear a room back to the studs to get rid of the odor.

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We used to get strays hanging out under our house from time to time. When it rained the moisture would bring out the smell even after they'd been gone for a while. Check to see if the underfloor area is accessible to cats.

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First check for leaks. In my bathroom that smell was coming from either wet water-damaged plywood underneath a leaking sink or the wet water damaged vanity.

If nothing is leaking check your drain traps.

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One time my friend spilled water on his carpet and it smelled like dog pee. Maybe you have wet carpet.

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The OP clearly states that the smell is in the bathroom (very likely not carpeted). – Doresoom Dec 10 '14 at 16:38

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