Dogs have a keen sense of smell and they often sniff people's crotches. There are a few reasons why dogs do this, including to identify their owners, to check for pheromones.
Dogs can identify their owners by their scent. When a dog sniffs a person's crotch, they are able to pick up on a variety of unique scents, including sweat, urine, and bacteria.
Pheromones are chemical signals that are released by animals. They can be used to communicate a variety of information, such as sexual availability, dominance, and stress levels.
Investigate new scents. When a dog sniffs a person's crotch, they are not only able to identify the person, but they are also able to learn about their recent activities.
Dogs may also sniff crotches as a way of marking their territory. When a dog sniffs another dog's crotch, they are able to pick up on the other dog's scent.
If a dog is feeling stressed or anxious, they may sniff crotches as a way of self-soothing. The scent of another person can help to calm the dog down and make them feel more secure.
In some cases, dogs may sniff crotches as a way of playing. This is especially common in puppies who are still learning about the world around them.