Whether they are happy to see you or stand guard in warning of danger, dogs use their noses to determine if something is to be feared or trusted. Have you ever wondered why dogs go nose to nose with other dogs, or nose to butt? Or why their noses are cold and wet? It turns out a dogs nose is like a wet sponge. Their noses have 300 million olfactory receptors that capture smells from the air. Compare this to humans which only have 6 million receptors means that dogs are 50X more sensitive to smells than a human. Their brain can distinguish smell in concentrations up to 100 million times less than humans can detect smells. If you could smell a teaspoon of sugar in one cup of coffee, it would be akin to a dog being able to smell 1 tsp of sugar in enough water to would fit into 2 Olympic sized pools. You may be aware of bomb sniffing dogs, drug sniffing dogs. There are even some dogs that sniff out cancer cells.
Taking a look at that beautiful nose!
The dog breathes in through the nostrils and exhales through the slits on the side of the nose. The two nostrils can operate independently from one another allowing the dog to locate the smell quicker. Dogs have the ability to inhale and exhale at the same time. Once inhaled, the air is separated into two parts. One part is for the smell and the other is for respiration. Dogs have a second scent receptor in their nose called the vomeronasal organ. This is solely dedicated to sniffing out phermones. This makes it possible for dogs to discern friendly animals versus potential predators, recognize human emotional sates and even notice when someone is getting sick.