Source: pmarkham, licensed under CC BY-SA 2.0
- A dog’s ability to recognize scents is approximately 1,000 times greater than that of a human being.
- Although people have less olfactory sensitivity then dogs, humans still have the ability to recognize some biological smells, including their dog
- A dog’s neuter status, diet, and housing conditions can make it easier or more difficult for its owner to recognize it by scent alone.
Human Noses Not So Bad
It will come as a surprise to many people to find that, although it is certainly the case that dogs do have a remarkable capability to detect and identify odors, it is nonetheless the case that human beings are not completely impoverished when it comes to this ability. The dog’s sense of smell has been estimated as being 1,000 times more sensitive than that of humans, at least for biologically related odors. The way that scents are processed in the human brain is also different from that of dogs. Generally speaking, for us, odors are often unconsciously registered, although they may still produce an emotional response. Under certain circumstances, especially if our attention is directed toward the odors and if we are forced to choose among them, humans do have a reasonable degree of accuracy in recognizing the scents of living things.
For humans, the sense of smell is often considered one of the least-important sensory systems; however, it still plays an important role in human life, especially in social settings. Each individual has a distinct odor that can be influenced by many factors such as age, diet, hormonal changes, and diseases or infections. It may even be the case that our scent changes in a detectable way depending upon our emotional state. This explains why people are often willing to spend extravagant amounts of money on perfumes to change their individual scent identity.
A number of studies have demonstrated that humans are able to recognize family members and also certain characteristics of other individuals based upon their smell. The studies that revealed this ability mostly used a similar technique. Specifically, the target individuals were asked to wear a T-shirt for a day or two, and then that T-shirt was sealed in a plastic bag. Later, other individuals were asked to sniff the contents of the bag and attempt to make a recognition. In this way, it was found that postpartum human mothers can accurately identify their own newborns by scent alone, and both mothers and fathers can correctly discriminate the odors associated with their own children. Furthermore, women are able to roughly categorize the age of strangers by their scent, dividing them into infants, young children, sexually mature adults, and elderly groups using only their scent as a guide.
Since our pet dogs live with us as virtual family members, and each has its own unique scent, it would seem to be a logical extension to believe that humans might similarly be able to recognize their own dogs by their smell. To test this, a group of researchers headed by Lucie Přibylová of the Department of Ethology and Companion Animal Science at the Czech University of Life Sciences in Prague enlisted 53 dog owners (40 female and 13 male participants of different ages). Instead of using T-shirts to gather the target scents, they used sterile gauze pads to rub down each dog and these were placed in separate glass jars with a twist-off lid.
Finding the Scent of Your Dog
The testing procedure was quite stringent. For each trial, six glass jars were randomly placed in a line up in front of the human participant. One contained the scent from the participant’s dog and the other five were scents from random other dogs. This was a double-blind experiment, meaning neither the dog owners nor the experimenters doing the actual trial were aware of which jar contained the sample with the scent of the dog owned by the person being tested. Later, the choices were decoded based on numbers placed on the jars. Participants were allowed to sniff for as long as they wanted before telling the experimenter the number code on the jar that they believed contained the scent pad that came from their own dog.
It turns out that the recognition ability based on scent was really quite good. Given the fact that there were six possible choices, the probability of choosing the correct one by chance alone should only be about 17 percent (or one out of six). The researchers found that men did better at recognizing their own dog by smell and were correct 89.5 percent of the time (that is nearly nine out of 10 times). Women were correct 64.7 percent of the time (which is nearly two out of three times).
Factors That Affect Accuracy
There were some other factors that also made a difference. Neutered dogs appeared to be easier to identify.
Dogs that lived outside were also easier to identify; presumably this is because, if you live in a house with the dog, you are exposed to its scent all the time and you may develop olfactory fatigue for that odor. This is much like if you walk into a house where cabbage is being cooked. You smell it immediately but, after a few minutes, you no longer smell the cabbage because your scent receptors have adapted to that odor.
An odd finding is that dogs that were usually fed dry food were more easily identified by their owners than dogs fed raw meat. The researchers suggest that this may be because the majority of their sample was women, and studies have shown that women prefer the scent of men who eat a plant-based diet to those of men who consume large amounts of meat, and that may be reflected in how they respond to the scent of their dogs.
A last finding of interest has to do with age — the age of the human sniffer, not the dog. In general, younger individuals were better at identifying dogs than older individuals. That means that the best dog identification ability was found in young male participants.
So it appears that humans can identify their own dogs when the only information they have is the dog’s scent. However, the researchers do not suggest that if your dog goes missing you should get down on your hands and knees and start sniffing for his tracks. By comparison, you should remember that, although the human nose is not relatively nonfunctional as some people believe, it is still 1,000 times less sensitive than the nose of a tracking dog.