We recently had two of our bathrooms tiled and my husband removed the toilets. He placed a rag in the drains and the toilets were out for about a week. The last one was replaced just tonight. We noticed a faint sewer smell that has increased and can now be smelled even in a bathroom we didn't remove a toilet from at all. We are hoping that now that both toilets have been replaced the smell will go away. What do we do if it doesn't? Is this harmful?

When you tiled the floor, did you put flange extenders on to bring the flange up flush to the floor? Did you install new wax rings? Sounds like a wax ring is not sealed properly. If the flange is not flush with the floor, the wax ring will not seat and sewer gas will leak into the room. Sniff around the floor joint with the toilet-smell it there?

Yes, sewer gas can be harmful, it could even explode if it is concentrated. Brian is steering you in the right direction. Your flange should be flush with the floor or 1/8" proud of the floor. If it is not add a flange extension or double wax ring if you are in a pinch. How to Install a Toilet Flange Extension | eHow.com