It’s always a surprise, and a bit embarrassing when a dog trots over and buries his nose in your crotch or up your butt.  When being searched in this manner, it’s hard to keep in mind that he isn’t trying to humiliate you, he’s merely searching for information.  Ever wonder what he’s looking for and, better yet, did he find it?
The sense of smell is a dog’s dominant sense therefore, when he is reading scents it’s like he is reading a written status report about whatever and whomever he is sniffing.
Apocrine glands are a special kind of sweat gland that produces chemicals called pheromones which convey social information.  These glands are spread over the entire body of dogs and other mammals with higher concentrations in their genital and anal areas.  Almost immediately, the secretions from these glands begin to form bacteria, modifying as well as intensifying the smell.  Pheromone scents identify the sex, age, and mood of the individual along with sexual information such as whether the female is pregnant, having a false pregnancy, or where she is in her menstrual cycle.
Dogs have a sort of pancake-shaped pouch of receptive cells called “Jacobson’s organ” or “vomeronasal organ” located just above the roof of the mouth for use as a special scent detection system.  It allows scent molecules to enter through both the mouth and nose.  This is important to the dog as there is a region in the olfactory bulbs in the dog’s brain that is dedicated to processing the information scent from this receptor,
The highest concentration of apocrine glands in humans are in the armpits and groin area.  These are the areas dogs will target when meeting strangers, especially if there is a sexual scent and/or women who are menstruating or have recently given birth and are still nursing their child.  A change in pheromones when a female ovulates will attract dogs.
Researchers, noticing a dramatic increase in crotch sniffing around ovulation, put the fact to use by training some Australian shepherd dogs to identify cows that had just ovulated, allowing successful breeding of these cows during their short fertile period.  This “dog sniff” test proved more reliable and easier to administer than most other methods of detection.  Do I smell a new class of assistance dogs for humans?
Nonetheless, having said all this, many people have strong negative reactions to scent messaging.  When I’m approached by a four-legged friend bent on rooting in my nether-regions, I often wonder if they find gold, will they share it with me.  In any case, when their done gathering their information, I never fail to ask them how I’m doing.