Dogs Like to Sniff Crotches
Humans are often embarrassed when a dog starts sniffing at their groin, or pokes its snout in their butt. The dog has no idea that placing its nose in these parts of the human body might be offensive. The dominant sense for dogs is their sense of smell. This is a common way to gather information from other dogs, and in many ways dogs treat humans as if they were similar to canines.
A special kind of sweat gland called apocrine glands produces scents that convey social information.
These chemicals are called pheromones. Dogs and most other mammals, have their apocrine sweat glands spread over their entire body with higher concentrations in their genital and anal areas. Pheromone scents not only identify the sex, age, health and mood of the individual but also carry a lot of sexual information as well.
In humans the apocrine glands are found only in certain areas of the body, with the highest concentrations in the armpits and groin area so dogs try to sniff these areas for the same reasons that they sniff the genital regions of dogs. As when meeting other dogs, strangers receive the most attention of this sort, especially if there is a tinge of sexual scent. People who have had sexual intercourse recently seem to attract this kind of attention from dogs.
The odors of bacteria
Although mammalogists tend to talk about the stinking secretions of these glands, the secretions themselves are largely odorless. At least in primates and dogs, the stink comes instead from what the secretions feed—bacteria. Each apocrine sweat gland feeds bacteria. These bacteria, depending on their species, mix, and abundance, produce the unique odor. In other words, your dog stinks because it feeds special bacteria that produce an odor that, in turn, communicates a specific message to other dogs.
Smelling the sick
The smells pouring out from various parts of the body are unique to an individual, made up of select compounds that vary depending on age, diet, sex, metabolism and health.
Some diseases result in a characteristic odor emanating from different sources on the body of a sick individual. A person’s smell escapes not just from their skin but their breath, blood and urine and subtle differences reveal just how healthy they are.
In more recent studies, researchers found that the disgust felt by people when smelling unpleasant odors activated a mild immune reaction of their own, to protect them from disease.
They tested immune reactions in people exposed to a range disgusting smells — including cheese, fermented fish and rotten yeast — and found slight increases immune activity. People’s bodies were gearing up for attack. Emotional disgust is there to keep us healthy.
Sorces: CNN, Scientific American, Psychology Today