It's pretty much the first thing that happens when two dogs meet: mutual butt-sniffing. This may seem disgusting or embarrassing to you, but your dog sees it differently. Why do dogs sniff each other's rear ends? Is this a healthy and normal thing to do? 

Your Dog's Sense of Smell

A dog's olfactory system is complex and advanced, making its sense of smell far superior to that of a human. To give you an idea of the difference, consider the fact that a humans has about 5 million olfactory receptors in the nose and dogs have about 220 million.

 Dogs can smell layers upon layers of scents even when we can smell nothing. That's an impressive nose.

If you had a nose like that, you'd probably want to sniff everything too! Dogs sniff their way through life for two main reasons:

1. Enjoyment: Stuff smells good! Smelling things is fun. Smelling feels good and stimulating.
2. Information: To figure out or learn more about something

Why Dogs Sniff Butts

Many people think of butt-sniffing among dogs as a type of greeting, but it's so much more than that. Through sniffing, dogs are able to learn things about each other. Every animal has his or her own unique scent: humans, dogs, cats, and so on. While you or I can only vaguely detect a personal scent, our dogs pick up a number of clues through their noses. These scents are especially potent around the genitals and anus (the location of the anal sacs, which collect odorous fluid). Scents in this area can tell another dog about gender, reproductive status, diet, health status, temperament, and much more.

A dog can also remember scents and therefore determine whether or not he has met this particular dog before.

So, when a dog meets another dog, they each have stories to tell. We humans make small talk at dinner parties. Dogs sniff one another's butts. It's normal behavior.

Many dogs also try to find out more about humans through, ahem, crotch-sniffing, often much to our embarrassment. Don't worry, it's not a problem with you -- it's just canine nature. Dog owners: if your dog is crotch-sniffing someone, please redirect him somewhere else! Try to discourage this behavior if you don't want people to hate your dog.

Should I Let My Dog Sniff Other Dogs?

If the dogs meeting are healthy, well-socialized and supervised, it's actually best to let them "sniff it out" as much as they want (provided each dog is tolerating it well). Dogs may actually be less likely to fight if they take an adequate amount of "getting-to-sniff-you" time with one another. However, some dogs can get intense with the sniffing while other dogs need their personal space. Watch the behavior and body language of all dogs. If one dog is overdoing it and the other dog seems annoyed or stresses, then the owners should call their dogs away. Also, it's ideal to let dogs meet and play in pairs. Dogs are more likely to get over excited in groups, which can lead to fights.