Pheromones are chemical substances secreted by an animal that influence the behavior of other animals of the same species. Unlike other hormones, pheromones are secreted externally and influence other animals, typically by smell. In this case, pheromones may play a very important role in animal behavior.
In dogs, pheromones probably influence group integration and are a factor in fighting and general aggressiveness. Some theories suggest that dogs release pheromones in urine and feces, and perhaps through exhaled breath, subcutaneous glands at the base of the tail and the foot pads. This would tend to explain why aggressive, fighting dogs are often compulsive urine sniffers and urine markers, and why they become less aggressive when sniffing and urine marking are not allowed by their owners.
Pheromones may act as a trigger or primer for certain types of behavior. This case is typical of many wherein a dog appears to sense, by smell, another dog that may be perceived as a threat. Also typical among some vicious biting dogs is the need to brand a strange territory with their own pheromones before launching an attack. Some take place even when the biting dogs were on their home territory. Remedial programs include restricting urination of the problem dog to a single area of his own yard. This tends to lower the aggressiveness, as well as reduce the incidence of household urination.