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Dogs sniff out others' identities

Original Publication Date: July 20, 2015
By C. Sue Furman, Ph.D.

It is normal for dogs to greet each other by sniffing butts. The snuffle is more than a doggie hello. They are gathering social information about each other from chemicals called pheromones given off by their sweat glands.

Dogs have two types of sweat glands. Eccrine sweat glands are present in the foot pads where they secrete a watery substance through pores that open directly onto the surface of the skin. You have probably seen a dog leave damp paw prints on the sidewalk on a hot day. They were simply sweating to cool themselves.

Apocrine glands are associated with hair follicles in the skin over the entire body surface, but are in high concentrations in the genital and anal areas of the dog.

These glands release pheromones that are basically odorless. Waiting bacteria immediately act on the pheromones. The result gives the pheromone a distinct and quite intense scent. The product is an odor that another dog can read just as you might read a postcard.

The canine has a very powerful sense of smell because their nose has up to 220 million olfactory receptors to detect odors. Human noses have 5 million to 10 million olfactory receptors.

Dogs not only capture scents, they can make sense of them in Jacobson's organ, a special scent detection system in the neocortex of the brain. It is about four times larger than the odor-processing area in the neocortex of the human brain.

Jacobson's organ allows dogs to interpret many pheromone messages that would go undetected by the human olfactory system.

A dog can sniff pheromones on another dog's butt and determine the sex, health, age, mood of the individual, whether a female is in estrus (heat) or pregnant, and no doubt much more.

A human might detect a smelly rear, but no social information on the dog's status would be revealed.

Humans also have eccrine and apocrine glands but the distribution is quite different from that of a dog. Human eccrine glands cover most of the surface area of the skin with the highest concentration on the palms of the hands and soles of the feet.

We also have apocrine glands that produce message-sending pheromones. These are found in the axillary (arm pit) and pubic regions of the body. A dog will probably not jump up to smell your arm pit, but they may nuzzle their nose in your groin or tush. They are not being fresh. They are just reading your pheromone messages.

It is embarrassing to meet a dog that greets you by sniffing your private parts, but it shouldn't be so surprising. Hopefully their owner will discourage their nosey advances. You on the other hand will know that they are just reading your pheromone signature.

Marvel at what amazing messages they may be interpreting from your chemical autograph.

Sue Furman, Ph.D, has published two books and a DVD on canine massage and teaches classes in pet massage, acupressure, first aid and CPR. See her schedule and submit questions at