What odors are hardest to clean your home from?

As for my, the hardest, in a way since it is the most consistent bad odor in the house, is smoke. Well, my fault anyway since when I used to smoke at home, I stay at the balcony. When the gentle breeze goes into the house through the balcony, the smoke goes in as well. When I come in after a stick or two, it doesn't smell good inside. I'm very particular since I am the only smoker in the house. I don't want them to inhale it. So far, I'm getting successful in quitting.

i guess for me the hardest is the urine..so strong...and i hate it when my children will not flash while using the comfort room ..

All of the above minus gravy (I like the smell of gravy) plus poop...yuk!

I think it's cat urine and smoke. When a cat has peed on a carpet, it's so difficult to scrub the smell out. It lingers there and encourages them to go there again because they can still smell it there even after our senses can't detect it. Smoke is the same. It lingers and gets into everything. It can take a long time to clear the smell out.