Can Dogs Smell Human Urine?

Do you have a dog that loves to sniff pee-mail?

If walks turn into dawdles because the dog has their nose glued to the ground, you'll be well aware of how nose-obsessed some dogs are. The observant amongst you may even have noticed certain patterns as the dog sniffs. 

For example, did you know that male dogs are more interested in sniffing pee from male dogs than females (unless the female dog is in heat)? Whilst female dogs are equally interested in both male and female urine scent signals. 

That's all very well when your fur-friend is reading the pee-mail left by other dogs, but have you ever wondered if they can smell human pee? 

Yes, dogs can smell human pee...it's just that (hopefully!) they don't get the opportunity very often. After all, most people are house trained and so the neighborhood should be unrewarding from a dog-smelling-human-pee perspective. 

When sniffing out pee, dogs follow a particular pattern. From some distance away they will pick up the hint of a scent to follow. They then move toward the smell at a good pace by sniffing as they go. What the dog does is to sweep with the nose from side to side in order to find where the smell is strongest. In science-speak, this is known as the 'deciding' phase. By moving towards areas where the scent is more concentrated, the dog naturally moves towards the source. 

Then, the dog enters the 'tracking' phase, where the dog concentrates harder on pinpointing the origin of the scent. To do this they move more slowly, usually about half the previous pace. But the payback is that the dog sniffs harder and for longer. By increasing the airflow across the sensitive mucosa that contains scent detectors, the dog is better able to read where to go. 

Finally, as they get right on top of the smell of human pee, the dog may flehman. This is where they lift the lip to expose special scent receptors in the vomernasal gland. These add detail to the scent picture, and are the equivalent of opening up a message in their email (or pee-mail) inbox to read the detail. 

For almost as long as dogs have lived alongside people, the awesome ability of our canine companions to sniff out scents and follow a trail has been evident. Time travel back 20,000 years and early man survived by hunting and gathering. Having a dog that was capable of tracking prey gave early man a huge advantage and could mean the difference between feeding his family or starvation. 

Look at cave painting and you'll discover how those nomadic early peoples used dogs to track and hunt. What's also likely is that dogs with the best tracking abilities (ie the best sense of smell) were highly prized and more likely to be used to produce the next generation of hunting dogs. 

Thus, in the earliest form of selective breeding and before actual dog breeds were a thing, man was selecting dogs with a good sense of smell. This is added to a dog's already way-superior sense of smell as an animal, raising them from amazing to superhero status. 

As more time passed, it became obvious that some dogs were better at certain tasks than others. This is where the differentiation between working dogs started to come in. Whilst some were bred to herd, and others to protect, others were bred to sniff and became tracking dogs. Many of these dogs with a superior sense of smell are to be found in the hound classification of the Kennel Club. 

Not only are dogs able to smell human pee, but they can detect specific scent notes within the urine. Thus, they can pick up the smell of hormones, sugar, and things like if the person has an infection or not. 

This amazing ability is down to the super-sensitive nature of the canine sense of smell. Again, this is due to the number of scent receptors in the canine nose, the anatomy of the dog's nose which maximizes exposure to scent, and the size of the scent processing center in the brain. 

For example, the total surface area of cells sensitive to smell in people is around 5-square centimeters; contrast this with the dog who has around 125-square centimeters or more. This is like having comparing an old-fashioned cathode-ray TV set with a modern, high definition TV. 

Sniffer-dogs are an important tool for finding dangerous substances, money, drugs, or even disaster victims. Indeed, dogs can be trained to be living smoke-alarms for deaf people or to sniff out cancer. To such a nose-sensitive animal teaching them to sniff out human pee is relatively straightforward. 

Teaching a dog to smell human pee is taught using a reward-based system. The idea is that when the dog correctly identifies human urine, you reward them. This makes them keen to track down the smell so that they can claim their next reward. Once the dog has made this leap, you can put the action of detecting urine on cue by adding a command word. 

The first steps are taught in a controlled way by having a rag soaked in human pee for the dog to sniff. As they sniff it to get the pee-mail, you say "Yes" in an excited voice and immediately give a reward (even though you are likely not excited about the pee-rag, yourself). For food-motivated dogs, that reward can be a small tasty treat. For other dogs who aren't bothered about food, you might play a game of ball or give them a toy they love. 

Place the rag in another location, but one that's still easy for the dog to find. As they approach in anticipation of the reward, say "Yes" and add a cue word such as "Track". Then praise them when they find the rag. As the dog becomes more accomplished, make the rag more difficult to find, so that the dog has to work his nose harder to track it. Before you know it, the dog is trained to smell human pee.