HOW DOES MY DOG SMELL? by Brian Holmes

I am very grateful to Brian Holmes, who studies MSc Applied Animal Behaviour & Welfare at Newcastle University, for agreeing to write this article about the science behind dogs using their noses.


by Brian Holmes © 2014 All Rights Reserved

is a UK Trade Mark #UK00003028207 of Dog Games Ltd




Perhaps the first thing to say when looking at how dogs use their noses is that we don't know the full story yet of what happens between sniffing and smelling and any resulting behaviours or responses that come from that information being processed in the brain.

Despite a widespread view of the incredible olfactory abilities of dogs, and an increasing usage of dogs in scent-related working environments over the last few decades, there has not actually been a huge amount of research to identify the limits of a dog's olfactory abilities. Although research efforts are reportedly increasing it leaves us with some substantial gaps in knowledge at this point in time.

A lot work on animal perception and processing of information taken in via the various senses has been done on mammals in general, rather than dogs specifically, so some leeway on potential differences between species should also be acknowledged.

Similarly, with the research that has been done we should note that there hasn't been a common approach on experimental methodologies for quantifying these capabilities so results have differed and might well be considered in more of a range than in absolute terms.

The 'science' behind how a dog smells also spans a number of different academic disciplines so the aim here is to take an overview of what we know about dogs and their sense of smell and walk on our tip toes across disciplines to try and get down a little bit deeper to gain an understanding of what we do know and how that is relevant to SPRINKLES (TM).

So, overall, we will cover some things that we do know and some things that we think we know about how our dogs smell.


Dogs live in an olfactory world. Their primary means of perceiving the world around them is through taking in smells from the environment through their nose.

These smells are used to detect prey or other foods via foraging (and is used in conjunction with taste for food selection), noticing hazards in the environment (anything from a fire to another predator), identification of others (e.g. family members), selection of mates, and smell is also important in communication. A whole chemical world of 'Pee-mail' and 'NoseBook' is out there invisible to us and is an area which we are only beginning to understand.


So how good are the olfactory capabilities of dogs? Researchers have found their ability to detect an odour was sensitive to one part per billion against a more concentrated distracting odour. Other research put their sensitivity to some odours at one to two parts per trillion.

Those kinds of numbers are hard to understand so consider some of the applications we have put dog's noses to as a way of understanding how incredible they are compared to humans.

Drug and explosive detection are well-known applications but there are also biomedical applications such as cancer detection for various types of cancers; seizure warning for epileptics and both detection and warning with diabetes. Other applications have included wildlife conservation whether that be detecting ribbon snakes in their natural habitat or determining if a bee hive is over a fungal or parasitic mite threshold, either of which could lead to a colony collapse. As well as cadaver dogs that search for dead bodies (or evidence of the presence of dead bodies) there are specialist cadaver dogs that can locate dead bodies underwater. That dogs can detect, discriminate and identify these scents is truly amazing.


It is an obvious thought that the basis of a dog's olfactory abilities compared to humans is structural i.e. they have a big nose compared to us! The simple truth is that they are designed for smell in a way our noses are not.

Clearly we can run into some breed differences so, generally speaking, dogs take in smells through their nostrils into a large nasal cavity which is lined with a mucosa in which a large number of olfactory receptor neurones sit on the olfactory epithelium (along with other cell types). Information gathered here via the receptor neurones is sent up to the olfactory bulb (part of the limbic system and the first sub-system involved in processing information sent from the olfactory system) towards various other structures in the brain.

For perspective the olfactory epithelium is approximately 3cm²-5cm² in humans but 75cm²-170cm² in dogs. Humans have somewhere in the region of 20-40 million receptor neurones to put to work on incoming smells but dogs have hundreds of millions running into billions of the same receptor neurones. Dogs also have a functioning Vomeronasal (or Jacobson's) Organ which serves particular olfactory functions relating to uptake of pheromones and a role in reproductive behaviour so mammals have two separate parts to their olfactory system where humans have one.

There is also a genetic role in olfactory ability with the number of actively functional genes within the olfactory gene repertoire significantly higher in dogs compared to humans. The number of olfactory receptor related genes is similar in dogs and humans but a much higher proportion of those genes are non-functional in humans - evidence that evolutionary adaptation has moved humans away from using their sense of smell as much as maybe we once did while domestic dogs still have well over 80% of the olfactory repertoire functional.

Even with nature providing a structure designed to smell the contribution of sniffing should not be underestimated as part of the overall olfactory capability as it facilitates taking in smells from the environment and transporting them through the nasal structures.


So, structurally, dogs are very well equipped for olfactory perception of their environment. But what happens after an odour is inhaled and how does that relate to SPRINKLES (TM)?

How olfactory information is processed, where in the brain it is specifically processed and what results on behaviour that processing then has are still developing areas.

Work has been done in other mammals such as mice although more work is likely to be done on dogs directly as non-invasive methods progress. While we do know a reasonable amount about where information is processed in general in the brain, and the role of neurotransmitters such as dopamine, the specifics of it are not there yet so the following concepts are theoretical. So while associated research does point to particular areas of the brain involved with these processes we will skip the anatomy of the brain here.

We think of activities dogs do, such as sniffing, as natural behaviours. Researchers such as Jaak Panksepp in his emotional model of animals proposed that, actually, it is more than that and mammals such as dogs are intrinsically motivated to undertake activities such as foraging and to search and explore their environment for the good things that are out there.

So this is not considered to be a simple reward system or a means to determine which kinds of foods are tasty, it is an intrinsic impulse to search, explore and make sense of their environment.

Another researcher, Berridge (and associates) has proposed a model, considered to be more balanced by some, which breaks down the concept of reward into three components: 'LIKING', 'WANTING' and 'LEARNING'

WANTING is more or less equivalent to Panksepp's SEEKING and is characterised by what Berridge terms 'incentive salience' - an intrinsic motivation that facilitates approach to, and consumption of, something rewarding.

Items such as food (so natural rewards) will stimulate WANTING and the resulting behaviours of searching, sniffing etc. These behaviours are self-stimulating so the animals are motivated to keep doing it. The actual 'reward' of finding something pleasurable is almost an interruption as a different (consummatory) system kicks in to process the act of consuming the reward, once it has been obtained. The LIKING response (following on with Berridge's approach) to the reward will, momentarily, inhibit 'WANTING' but, in our case, the dog will return to moving around foraging again.

Both Berridge and Panksepp agree that what really motivates animals to do things, including learning, is the anticipation of achieving a reward as opposed to consuming it. So WANTING/SEEKING are more important, or perhaps relevant, to the animal than LIKING - the response that occurs when the reward is obtained and consumed. Searching and investigating the environment is self-stimulating on an ongoing basis where a reward is a moment of pleasure.

An interesting sidebar on this relates to Simon Gadbois' 'Dopamine Hypothesis'. In his work on dogs undertaking scent work he found that traditional scent dogs such as hounds were not best suited to the work he needed them to do. While they had an incredible level of olfactory ability, it was not matched by the same level of motivation. The 'Dopamine Hypothesis' suggests that certain breeds have higher baseline levels of dopamine, the central neurotransmitter used in WANTING/SEEKING, and therefore important in olfaction and olfacto-motor behaviours (e.g. sniffing), which means that those breeds such as Border Collies tend to have a better all-round package of olfactory ability and work ethic to meet the demands of professional level scent work. So if you have a Border Collie, Siberian Husky, Jack Russell or Parson's Terrier for example….you are on to a winner. For the rest of us, it's interesting, but means that our dogs will work for SPRINKLES (TM) because it is intrinsically and consequentially rewarding to do so although, as with most things dog, they will all do it differently!

But what Gadbois suggests from this is that the 'software', i.e. the dopamine levels and neural mechanisms are more important for these behaviours than the 'hardware'.

Gadbois & Reeve also put forward the idea that olfactory information is processed in a similar way to visual information (Schneider's WHAT? And WHERE?). For olfactory information the WHAT? system covers Detection, discrimination and identification of scents and a WHERE? System applies to being able to find the location of an item such as food.

So a dog can detect an item such as a SPRINKLE, discriminate it from any other scents around it that may be similar and, essentially know that is the item it is looking for. Although we know that canids are good at finding items like food but how they do it in the absence of other perceptual inputs (such as being able to see or hear the source) is still unknown and shows these processes to be yet more complex) so WHERE and beyond still has mysteries to be unlocked.


We have seen that dogs are designed to interact with their world primarily through their sense of smell. They have incredible abilities which we still do not fully understand the extent of. We have also considered that while the brain structures involved are generally known the specifics of how and where this neuro-cognitive processing of information occurs but what is known has led to the developing of concepts such as WANTING and SEEKING which show us that dogs are intrinsically inclined to sniff and search their environment for the good things contained within and that ability can be harnessed for pet dogs with activities such as SPRINKLES (TM)



The images & material contained herein may not be copied or reproduced either physically or electronically without the prior individual written approval of the Author - Brian Holmes © 2014 All Rights Reserved.

"SPRINKLES"(TM) is a dog training UK Trade Mark #UK00003028207 of Dog Games Ltd - All Rights Reserved