Our helpline: 01803 612772

Developed and made in the UK. Patent numbers: GB2474042 • GB2535916

The nose that knows

A dog’s breathtaking world of scent

by Kate Mallatratt A Dip CBM, PPG, Canine Behaviourist

This article was first printed in Animal Therapy Magazine Issue 14 Autumn 2018 pp 20 – 23. Reproduced with kind permission from the editor. To visit their website, please go to: www.animaltherapymedia.co.uk

A dog’s nose is his primary sense © Bounders Dog Photography

“We might notice if our coffee’s been sweetened with a teaspoon of sugar; a dog can detect a teaspoon of sugar in a million gallons of water: two Olympic-sized pools full.”

Alexandra Horowitz: The Inside of a Dog:
What Dogs See, Smell and Know

Dogs have the most amazing sense of smell. In The Man Who Mistook His Wife for a Hat, neurologist Dr. Oliver Sacks writes of a medical student who took recreational drugs and dreamt he was a dog. The student woke with dog-like senses including a heightened sense of smell and could identify patients by scent, smell their emotions and pinpoint places by odour. Inanimate objects took on emotions and he describes “the happy smell of water…the brave smell of a stone”. This medical student offers us a window into our dog’s world, where scent is colourful, meaningful, evokes strong emotions and relays vital information for survival. In fact a dog’s sense of smell is so acute that it is thought he can pinpoint individual odours. Chicken broth, for example, would smell of meat and carrots and onions and stock: each ingredient having its own specific identity.

As humans relying heavily on sight it is hard to imagine scent influencing every activity, so let’s examine how a dog’s olfactory system differs from ours and why they can perform remarkable feats using smell.

The mechanics of olfaction
About one eighth of a dog’s brain is dedicated to scent. The olfactory bulb, where information about odours is processed, is about the size of a plum in dogs, whereas in humans it is the size of a raisin. Dogs can detect odour molecules 10,000 to 100,000 times lower can we can. The olfactory epithelium contains neurons and supporting cells, and a dog has between 220 million and 2 billion olfactory neurons while we have a mere 12 to 14 million. Pigment in the olfactory areas plays a part in a dog’s scenting skills too: dogs with richer brown pigment have superior scenting ability to albino dogs who lack skin and hair pigment.

The greasy smears left on the windows by your dog’s cold wet nose are due to the secretion of a thin layer of mucus covering the nose. This moisture helps to trap scent molecules more efficiently, and dog may lick a dry nose to aid scenting. Dogs wiggle their nose when scenting, opening and closing the side slits. They have sweat glands on their nose and these, combined with the respiratory turbinates (bony scrolls) within the nasal chambers that warm or cool air passing through, help maintain body temperature.

Sniffing causes air to be taken into the nostrils and over the bony subethmoidal shelf as it travels to the scent receptors. Scent molecules dissolve and stick to protein receptor cells in the olfactory epithelium that are sensitive to particular chemicals, and this determines their ability to detect certain scents. Each neuron expresses one type of receptor, and neurons sharing identical receptors send their messages to the same part of the brain. Scent molecules travel to the olfactory bulb, to the primary olfactory cortex and to the thalamus, which transmits them to the orbitofrontal cortex for processing. Signals also travel to the amygdala, hippocampus and other areas of the brain processing emotion. It is thought that scent memory lasts for life and so, for example, when my Golden Retriever met her daughter for the first time in five years there was instant recognition and none of the usual sniffing rituals that unfamiliar dogs display.

‘Licking’ scent
Along with most reptiles, amphibians and mammals, dogs have evolved a second olfactory system called the vomeronasal (or Jacobson’s) organ, and you may be familiar with this when you see your dog licking the air or mouth-smacking. This action is called the flehmen response and allows scent particles to be captured by the tongue, opening tiny ducts in the roof of the mouth (behind the front teeth) to allow species-specific chemicals such as sex pheromones to access the vomeronasal organ. (Non-pheromone scents such as food are recognised by the olfactory epithelium.) Search dogs are seen to lick as scent article as if to get extra information. The vomeronasal organ has its own nerves leading to the part of the brain devoted to interpreting its specific signals, and even allows dogs to smell under water. Thanks to the ability to draw in scent through the two tiny holes in the roof of their mouths without inhaling, dogs are able to locate scent through their open mouth when diving in water.

As we have learned, a dog’s nose is his most important sense and we can even influence his mood and wellbeing with scent however not all scents are mood- enhancing.

Chemical odours
We frequently fill our home with aromas that can negatively impact our dogs. Air fresheners, aerosol sprays and scented candles are examples of indoor pollutants that may disturb their ability to discriminate scents. Synthetic perfumes can contain toxic chemicals linked to hormone disruption, and some chemically scented flea or herbal collars are thought to adversely affect a dog’s ability to smell. Limit your dog’s exposure to strongly perfumed washing powders and conditioners when laundering dog bedding or dog coats by moving to natural chemical- free products.

Moving away from toxic scents there are many others, both man-made and natural, that can positively influence your dog’s mood.

Calming scents
Odours that have a soothing effect are useful for behaviour modification. For instance one product on the market diffuses comforting man-made pheromones and another uses natural oils that enhance the production of the calming neurotransmitter GABA. Some essential oils are considered toxic however others can positively affect mood and a study in the Applied Animal Behaviour Science Journal (2005) found that both lavender and chamomile reduced barking and movement in shelter dogs compared to those breathing fresh air, while peppermint and rosemary increased activity and noise1.

Aside from scents that calm, nose work activities can play a crucial part in wellbeing.

Foraging behaviour fires the seeking circuit, a reward system in the brain that drives dogs to search for food. Foraging can be a welcome distraction from unwanted behaviour such as humping or barking, or useful for calming a puppy’s ‘mad five minutes’. Foraging is stimulating for dogs with sensory impairment such as deafness or blindness, and finding treats hidden in a snuffle mat is a handy distraction while grooming. Hunting tit-bits thrown on the ground outdoors can defuse potentially challenging situations such as meeting a horse or a jogger when on a walk. (Tip: when asking your dog to find dropped treats, tap your foot on the ground near the treats rather than point with your hand, which brings your dog’s focus downwards.) Foraging can also provide gentle weight-bearing exercise and mental stimulation for dogs who are on restricted exercise due to medical needs.

Another group who can benefit greatly from nose work are senior dogs.

Scenting for seniors
As their eye sight starts to fail, hearing becomes impaired and cognitive function declines, smell is the one sense that appears to remain the strongest and therefore increasingly important. Just as we might complete The Times crossword daily to keep our mental faculties sharp, introducing regular scent work for senior dogs not only helps cognitive function but can provide gentle exercise. A few highly scented tit-bits folded into a blanket or tossed in the garden for foraging, or kibble dinner served in a snuffle mat, can enrich their day immensely. When my 17 year old Springer lost interest in eating from his slow feeder bowl and Kong, he cherished scent games.

Working dogs
With about 30% more genes devoted to olfaction than humans possess and around 40% more of the brain devoted to odours than a human’s, our dog’s powerful sense of smell has been harnessed to help people in many walks of life. Detection
dogs in particular carry a heavy responsibility in saving lives: they
can track criminals, find missing persons and cadavers, detect diseases and alert owners to life-threatening medical conditions, search for drugs and indicate landmines. Some dogs are trained to find luxury food and the Lagotto Romagnolo is specifically bred to hunt ripe truffles, a rare type of fungi growing underground on tree roots.

Miniature Daschund puppy Herbie enjoys scent enrichment games with a Snuffle Mat and PickPocket search mat (food is hidden in the pockets), and relaxes after foraging. © Shelley Morton

Enriching lives
Scent games, competition tracking and feeders involving seeking are all ways in which we can enrich our dogs’ world through scent, but perhaps one of the easiest and best ways is to allow him to sniff on walks for as long as it takes to ‘read the paper’. And as we wait patiently we can only wonder at how the scent makes him feel, imagine what information he is gleaning and second-guess how the ‘braveness’ of grass covered in morning dew might smell, or the ‘happiness’ of a new shoot emerging after a long, hard winter.

Search & Rescue Dogs
by Kathy Donaldson, trainee handler

Golden Retriever Rufus finds his ‘missing’ person after a 10 minute training search in the Brecon Beacons and is rewarded with his favourite toy: a fluffy tuggy on a bungee  © Kathy Donaldson

Using dogs to find missing people in the UK dates back to the battle fields of WW1 when dogs carrying first aid kits located injured soldiers by airborne scent. In 1965 Scottish mountaineer Hamish MacInnes founded the
Search and Rescue Dog Association (SARDA) based on the Swiss concept
of using dogs to find people buried in avalanches. Dogs are now used by many more organisations than SARDA, for example Lowland Rescue.

In Britain search dogs are used to detect deceased people both on
land (cadaver dogs) and under water (drowned victim dogs) and people who are, thankfully, alive (air scent dogs). Trailing dogs can follow the path of a person several hours after their passage (scent specific trailing dogs).

Search & Rescue training uses positive reinforcement and the dogs search for a person who carries their reward, usually a toy. They need a good level of obedience and to show no interest in livestock or wildlife when working at distance. Early learning pairs human scent with the reward, and a helper plays with the dog and then hides up wind whilst the dog watches, restrained by the handler. On release the dog will follow the cone of scent coming from the helper and on finding him that all- important game ensues. Soon the dogs understand the concept and search by scent alone, for them finding a missing person is just a big game of hide and seek that culminates in tremendous fun.

As training advances the dogs learn to return to the handler and give a clear indication that they have found someone, and then lead the handler to the missing person, or in the case of disaster recovery dogs, stand and bark at the location of the scent. Training involves generalising their learning to new environments and developing search stamina. Dogs train twice-weekly and it typically takes two to three years to qualify. For a SARDA assessment, a dog searches four different 20 hectare areas over two days, each search taking approximately 90 minutes and they must locate the ‘missing’ bodies.

Golden Retriever trainee Search & Rescue Dog Rufus, owned by Kathy Donaldson.    © Ian Roberts Photography

Each branch of scent-work involves specialised training with a rigorous certification process before the dog is qualified for a real search because, in many instances, the information the dog provides can mean life or death for the missing person.

Today there are around 150 volunteer search and rescue dogs covering the UK. Originally German Shepherds were the most popular breed, gradually being replaced by Border Collies and increasingly working Labradors and Springers. Golden Retrievers are rare, however along with my young Working Golden Retriever (WGR) Rufus, we are a trainee SARDA air scent team learning to detect live missing people. There are two other trainee WGR teams and, coincidentally, the dogs all have the same sire.

Rufus is a typical WGR: boisterous and playful, but with a sensitive side. At the end of a busy day his idea of bliss is to cuddle on your lap, although at 27kg it’s a bit of a tight squeeze! He has a huge desire to please and a great appetite for work, and I’m hoping that these traits will lead us to become a successful team.


Kate Mallatratt is a founder member of International Canine Behaviourists and is a member of Pet Professional Guild for force-free training. She is the author of Home Alone – and Happy! and worked in television as an assistant animal trainer for Plimsoll Production. Kate holds an Advanced Diploma in Canine Behaviour Management and specialises in errorless learning, a concept she incorporates into problem prevention, behaviour modification and enriching the home environment for the family dog. Kate has owned and trained dogs for many years and runs her behaviour and training business, Contemplating Canines, in East Devon, UK. In 2017 she founded PickPocket Fabric Food Foragers, a company making fully washable foragers for dogs.


Barth, F G et al (2003).Sensors and Sensing in Biology and Engineering. Springer- Verlag, Wien, Austria.

Beaver, B V (1999). Canine Behaviour: a guide for veterinarians. W B Saunders Company, USA.

Becker, K DVM (2017). Favorite Household Products you should Pitch in the Trash Today. Available from https://healthypets. mercola.com/sites/healthypets/ archive/2017/12/10/chemical-air- scenting-products.aspx

Farrer-Brown, G Dr (2017). The Dog’s Nose. Available from https://www. medicaldetectiondogs.org.uk/the-dogs- nose-2/

Gazit, I & Terkel J (19 November 2002).

Explosives detection by sniffer dogs following strenuous physical activity. PhD dissertation, Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel. Available from http://www.appliedanimalbehaviour. com/article/S0168-1591(02)00274-5/ abstract

Hepper, P G & Wells, D L (28 November 2005). Perinatal Olfactory Learning in the Domestic Dog. Oxford Journals,
Life Sciences & Medicine, Chemical Senses, Volume 31 Issue 3. Available from http://chemse.oxfordjournals.org/ content/31/3/207.full.

Horowitz, A (2009 2nd edition). The Inside of a Dog – What Dogs See, Smell and Know. Simon & Schuster UK Ltd, London, UK. P72.

Laurence, K (2012). Intelligent Dog Training e-Course. Course Notes. Canine On-Line Learning And Resources, Learning About Dogs Ltd, UK

McConnell, P B PhD (2007). For the Love of a Dog. Ballantine Books, Random House Publishing Group, USA.

Miklósi Á, (2009). Dog Behaviour, Evolution, and Cognition. Oxford University Press, Oxford, England, UK. Reber S R, Allen R & Reber E S (2009 4th edition). Penguin Dictionary of Psychology. Penguin Group, London, England.

Sacks, O (1985). The Man Who Mistook His Wife For A Hat. MacMillan Publishers, London, UK.

Syrotuck, W G (200). Scent and the Scenting Dog. Barkleigh Productions, Pennsylvania, USA.

Zug, G R (2 May 2008). Jacobson’s Organ. Encyclopaedia Britannica, Chicago, Illinois, USA.


1. Graham, Wells, & Hepper (2005). The influence of olfactory stimulation on
the behavior of dogs housed in a rescue shelter. Applied Animal Behavior Science, 91(1-2), 143-153.