For any enthusiastic cat owner, one of the most mysterious and intriguing aspects of the feline universe is the concept of communication via scent. Not only can cats leave their scents behind through various body parts, they can also do so by urine marking, a concept very foreign to humans.
Scent Gland Secretions
It isn't just male cats that secrete distinct odors for communication purposes. Female cats also do the same. Cats all possess scent glands throughout their bodies, on their tails, faces, paws and feet. They rub these body parts up against things in order to mark their turf. Cats are extremely territorial creatures, and scent secretion is the way they claim ownership of something, whether it's a person, a trusty old living room sofa or even a door! If your cat is rubbing up against your legs rigorously, it isn't necessarily a sign of affection, but rather one of owning you, which is rather endearing too in its own way.
Urine marking is a territorial and mating behavior that is exhibited both by male and female cats, although more often by reproductively mature males. Urine marking behavior is especially common in tomcats that have not been neutered. When a cat sprays his urine, he is leaving his scent behind for others to pick up on. He could be promoting his presence and desire to mate to any nearby queens in the area. He could also be doing it to show another male exactly who is boss, and warning the other to back away from his territory immediately.
When a human detects the odor of male cat urine, it can smell very strong and unpleasant -- very icky on your furniture and walls indeed. The scent is disagreeable due to its chemical content. It isn't just ordinary urine, but rather urine that is intended to chemically express feline communication.
If you've just about had it with your cat's noxious scent secretions around your home, one thing you can do that may minimize the issue is to get him neutered -- pronto. Since humans can't really detect the odors cats secrete through their body parts, the main problem generally is urine spraying. Also, because urine marking is often a mating behavior, neutering your tomcat will probably completely eliminate it. However, some cats do continue the behavior even after neutering as a result of old habit and routine.