Dogs rely on their sense of smell to identify people and learn things about them, especially people they do not know very well. Dogs have an extremely powerful sense of smell, and canines use their olfactory power to recognize people and ascertain things about their environment.
According to the Purina website, dogs have 220 million olfactory receptors, which is 44 times as many olfactory receptors than humans possess. Dogs have the ability to recognize people and other dogs by scent, the same way that humans use eyesight. Dogs also have a remarkable memory for smells, and do not tend to sniff people they know as much as people who are unfamiliar to them.