There are two sources of odors associated with urine. The first comes from bacteria that grow abundantly in dark warm places with a never-ending food source. A pet can feed the bacteria daily! This bacteria growth and breakdown of the urine creates amino acids.
These complex organic compounds will often work deep into the fibers to a point of becoming part of the fiber. This can present a challenging situation. The waste materials and gases from the decomposing urine create an unpleasant odor. When dried urine is re-moistened, it gives off ammonia gas. If smelled once it is seldom forgotten.
The second source of the odor is a chemical odor that is present even when the bacteria have been killed. This explains the reason that more than sanitizing is necessary to neutralize odors from urine. Urine also presents additional odor problems when the relative humidity is high. The salts and crystals that are left behind as the urine dries are hydrophilic and draw water to them. Dried urine is often easy to smell in the humid months because the salts attract the moisture, the moisture evaporates putting out a greater proportion of odorous ammonia gas. You must get rid of the urine salts in and under the carpet to get rid of the odor. That’s why cleaning existing urine spots WILL NOT remove any associated odor. In fact, it could INCREASE the odor in the air space for a temporary period of time