Odor in Bathroom

New-ish homeowner here. I didn't notice any odor in my bathroom for the 1st 6-8 months I owned it. But for the last 9 months I've noticed an odor that comes & goes in my bathroom. It is a strong urine odor. I live alone, and I'm female, so I'm pretty sure that I'm not missing the "target" of the toilet bowl. I did some sniffing around and found the the odor is the strongest coming from the air vent. It's gag inducing. I've cleaned the vent as much as I could reach and that helped, for a while. But the odor keeps coming back. At this point I know I need to call in an expert, but I have no idea which expert to call. Do I call in a plumber to see if any of the sewer venting is cracked? or do I call in a heating/cooling person to check my vents? Thanks in advance for any advice!

Exactly where is the vent? What type of vent? If it is an air conditioner vent on the floor right next to the toilet, an overflow may have gone down in there. Someone may have missed the target etc. When you were sniffing, it may not be from the vent but it might be the wax seal under the toilet is not sealing. If it is a dirty floor vent , you could have some of the vent replaced. You may need to pull up the toilet and replace the wax ring and clean under the toilet in case it is dirty under the toilet etc. A little more info or some pictures might help.

Thanks! The air return vent is opposite the toilet. I lifted the vent up and noxious "fumes" came out. I clean regularly around the base of the toilet & never notice a smell there, but the cleaner could mask any smell.

You may need BOTH persons. It sounds like a condensate drain may be improperly connected to your waste system. That can cause such odors. A plumber would be the first call. He can find the culprit, and may be able to fix it without calling the HVAC guy.

We do suspect the odor would be "sewer" meaning the rotten egg smell. Any urine in the waste line is usually diluted way below the odor point. That is why, as you commented on....our first supect if it is actually a urine smell is a "missed target"!

Do you have a bathtub, shower, or even a second lavatory which is not frequently used?