Cat urine odor is the result of ammonia, mercaptans, amines and skatole gases release from urine and feces. That kind of cat urine odor that is not cleaned can increase in concentration and eventually cause health problems to animals, but also humans. Studies have shown that even some ammonia can cause damage to respiratory tract, reduce weight gain and also cause extra stress not only to cats, but also dogs.
The main parts of cat urine are urea, the urochrome and the uric acid crystals and salts.
Most of the cleaning products will work on the first two parts mentioned above and therefore can clean the stain and some of the odor. But the cat urine odor cannot be fully cleaned if the crystals are left behind after cleaning as the dry and become dormant. When the carpet of wherever the crystals have dried becomes wet again or even just a little humid the odor comes back.
Therefore it is a very good idea to avoid the cat urine odor in your home to first of all teach your cat to use a litter box. Most cat litters do hold the odor in and the boxes are very easily cleanable. Do whatever it takes to train your can to use his litter box and cat urine odor is no longer a big problem.