When a dog smells your crotch, it is using its highly sensitive nose to gather detailed information about you. Dogs have an extraordinary sense of smell, with up to 220 million scent receptors compared to about 5-6 million in humans, and a brain region devoted to analyzing smells that is about 40 times larger than ours
. The crotch area contains apocrine sweat glands that release pheromones- chemical signals that convey information such as age, sex, mood, health status, and reproductive condition. Because these glands are concentrated in the groin and armpits, dogs sniff these areas to learn about a person, similar to how dogs sniff each other’s rear ends as a greeting and information exchange
. Dogs may be especially interested in sniffing the crotch if a person is menstruating, has recently had sexual intercourse, or has given birth, as these conditions change the pheromone profile
. This behavior is instinctual and a natural way for dogs to "say hello" and perform a background check on new individuals they meet
. In summary, crotch sniffing by dogs is a form of communication and information gathering driven by their powerful sense of smell and natural instincts to detect pheromones from sweat glands concentrated in that area
