Dog vs. Human: Who Smells Better?

22-02 four-dog-snouts

Photo above from:

22-01 human nose                     22-03 another Human Nose

Nose on left from:

 Nose on right from:

The post from March 9, 2016 (The Pug Smells!) focused on how dogs with small, short snouts, such as pugs and their brachycephalic brethren, cannot detect scents as well as dogs with large, long snouts, such as Basset hounds and bloodhounds. You may recall that pugs’ snouts simply don’t have enough space to accommodate as many scent receptors as those of bigger dogs. (With the sense of smell, size evidently does matter.)

Nevertheless, in comparison to my own ability to detect scents, even pugs excel. Their noses easily detect odors (particularly of edible items) that I don’t even notice. In fact, scientists have learned that a dog’s sense of smell is 10,000 to 100,000 times as acute as that of humans.

A couple of scientists put this difference into perspective:

Working from the lower estimate of a dog’s sense of smell being “only” 10,000 times better than that of humans, the former director of Florida State University’s Sensory Research Institute, James Walker, explained, “If you make the analogy to vision, what you and I can see at a third of a mile, a dog could see more than 3,000 miles away and still see as well.” (cited in Dogs’ Dazzling Sense of Smell by Peter Tyson, NOVA scienceNOW, posted 10/04/12 at

Another analogy is provided by Alexandra Horowitz, an animal behaviourist who studies dog cognition at Barnard College in New York City: “We might notice if our coffee’s been sweetened with a teaspoon of sugar;”22-08 coffee-cup

Photo from

[but] “a dog can detect a teaspoon of sugar diluted in a million gallons of water: two Olympic-sized pools full.”  (Inside of a Dog: What Dogs See, Smell, and Know. 2009. Scribner. p. 72.)

   22-09 swimming pool - Copy     22-09 swimming pool - Copy

Photos from

The difference in smelling ability between humans and dogs is partly due to the number of scent receptors: about 5 or 6 million for a human vs. 100 million or more for a dog. But a dog has other anatomic and physiological advantages as well. These advantages are explained by Tyson (cited above) and by Horowitz (cited above, pp. 67-74.) I’ll try to summarize these advantages here:

First, unlike a human’s nose, a dog’s nose stays wet.

22-11 wet nose   Photo from

Airborne odor molecules stick to the wet nose, and they’re easily licked into the mouth. From there, they’re carried on through the rest of the dog’s olfactory apparatus.

But before the scent molecules move much past the nostrils, the dog can sniff and snort and move the scent-laden air around. He can also widen or narrow his nostrils to help direct the air flow. A dog’s nostrils, unlike those of humans, are open at the sides; they look somewhat like vents.22-12 nose vents
22-13 nose vents

(Brown dog nose from and black dog nose from Black Dog’s Black Nose on the End of His Black Snout, by Quin, Liam R.E.: Mars and Reuben (2007) at×683.html)

The anatomy of a dog’s nostrils actually helps make it possible for him to know which nostril an odor enters from! So, from the very beginning, a dog has a great clue to which direction he should go to find the source of an incoming odor.

Moreover, as the air enters a dog’s nose, it doesn’t just go straight through the throat to the lungs, as ours does. Instead, it splits along two separate pathways: Part of it goes to the lungs for breathing, and part goes to the dog’s olfactory area, which is loaded with scent receptors. (You can find Brent Craven’s excellent copyrighted diagram of the two air flow patterns at

When the odor-laden air gets to the back of a dog’s nasal passage, it encounters the vomeronasal (or Jacobson’s) organ. This organ is especially sensitive to pheromones released by other animals, often in their urine. Pheromones are hormone-like chemical substances that convey information about the sex and sexual readiness of the dog who released them.

22-14 vomeronasal organ

Diagram from

(Obviously this diagram is not of a pug!)

A dog has still more advantages in the sense of smell. With vision and hearing, the input must be processed through intermediary organs (in the eyes and ears) before it goes to the brain. With the sense of smell, however, a dog’s nose receptors have a direct route to the specific area of the brain where olfactory data are interpreted. As Alexandra Horowitz says, “[The dog’s] nose is also the fastest route by which information can get to the brain.” (Inside of a Dog: What Dogs See, Smell, and Know. 2009. Scribner. p. 72.).

And – if that weren’t enough – the olfactory section of the brain is “approximately 40 times larger in dogs than in humans, relative to total brain size.” (from The Dog’s Amazing Nose! at ).

So it’s no wonder that our pugs astound me with their ability to out-smell me every day (not that I want to be able to smell everything that they can).

17-01 Sarah & Harley pee

But what do they really smell for when they search for the perfect place to pee?



The Pug Smells!

Do you know how a pug smells? If you’re expecting a discussion of the odor of a pug, that’s very simple: It depends on what the little critter has gotten into and how long ago he had his last bath. But today’s topic is the sense of smell.

Previously, I’ve focused on some health effects of the pug’s squished snout. That short snout also affects how well the pug can smell. That’s because the ability to detect odors is determined largely by the number of scent receptors in the nasal passages, and the number of receptors is largely determined by the size and length of the nose and snout; it’s a matter of the amount of space available for the receptors.

Obviously, a dog like the Basset hound has a bigger and longer nose than either the Boston terrier or the Pekingese, all shown below.

21-00 basset

Basset photo above is from


21-02 Boston terrier

Boston terrier photo above is from


21-03 Pekingese

Pekingese photo above is from

Dogs with larger noses and longer snouts have more nasal space and thus, room for more scent receptors. Therefore, such dogs are better able to distinguish smells than are dogs with smaller noses and shorter snouts – such as, of course, pugs.

21-04 Bloodhound

For example, scientists have determined that bloodhounds, being large, with long noses, have about 300 million scent receptors. (Bloodhound photo above is from

21-05 Benji

On the other hand, dachshunds, being small, but with long noses, have about 125 million scent receptors. (Dachshund in photo above is our pugs’ friend Benji, who is able to detect odors that they miss.)

Based on the facts above, I’d “guesstimate” that small, flat-nosed dogs like our pug Sarah may have as few as 100 million scent receptors. Here’s Sarah again (below), with a frontal view of her squash-nosed self:

21-06 Sarah cuddle bed crop 2

Lest you grieve overly much for Sarah and her brachycephalic kin, bear in mind that in a sniffing contest between a pug and a human, the pug always wins. Humans have only 5 to 6 million scent receptors, compared to my “back of the envelope” estimate of 100 million for pugs. Sarah may not be able to track an escaped convict through the Everglades, but she always knows when my pocket contains an empty plastic bag that once held dog cookies.

And whenever a morsel of food rolls under the stove or anywhere else that her truncated snout can’t reach, our pug Sarah knows it’s there. She places herself in front of the offending appliance or furniture and “points” her unpointed nose in its direction until she can get a human (usually me) to fish out the crumb for her.

21-07 Sarah smells

For more information about the dog’s sense of smell, read the chapter titled “Sniff,” pp. 67-88 in Inside of a Dog: What Dogs See, Smell, and Know by Alexandra Horowitz. (2009). Scribner.

The Very Best Ear Cleaner

When I’m confronted with cleaning multiple pugs’ ears, I often miss one of my pre-pug dogs, a little mixed-breed named Lapsi (pronounced Lopsy). The reason for this will become clear in a moment.

Here’s Lapsi as a puppy.

20-1 Lapsi puppy

Lapsi was a short-legged fuzz ball with a slightly curly, coarse and bristly coat. By the time she was an adult, her two-inch-long, grayish-blond hairs stuck out all over her body, making her look as though she’d sprayed her hair with a fixative without first brushing it – or that she’d stuck her snout in an electric socket and then used hair spray on it. Unfortunately, I have no good photos of Lapsi, for I had only disposable cameras in the pre-digital years that she graced our family – and I was a lousy photographer.

Here’s Lapsi as an adult.

20-2 Lapsi fuzzball.

Lapsi’s most remarkable characteristic was that she was consumed with the need to clean all the resident dogs’ ears (and we had up to 5 others, including foster dogs, in addition to Lapsi). Her obsession extended to the hygiene of the other holes in her canine friends’ heads: Along with their ears, she washed everyone’s eyes and nostrils at least once daily. She did this with her extremely agile and incredibly long tongue. I once saw her trying to extend her cleaning (and her tongue) into her best dog-friend’s mouth.

The friend, Tatiana or “Tat,” was the consequence of a late-night lustful assignation between a show-quality female Basset hound and a fence-jumping male Labrador retriever. She’d inherited the face and golden-brown coat of her Lab sire, or father, along with the short, crooked legs and drooping ears of her Basset dam, or mother. Actually, she looked like a Lab whose legs had been sawed off half-way. After meals, she also bore a remarkable resemblance to a very fully-stuffed sausage, elevated on top of four short stumps.

Tatiana, or Tat, the Grande Old Dame of the House

20-3 Tat sit

Tat, the Grande Old Dame of the house, stoutly refused Lapsi’s proffered service of a mouth cleaning – evidently she did not want to surrender any food crumbs that might still be there. Otherwise, Tat appreciated her little roommate’s cleaning services.

Given the opportunity, Lapsi would happily bathe the cranial orifices of humans as well as dogs. In unguarded moments, I briefly experienced Lapsi’s cleaning technique for the ears and nostrils. I definitely did not find the procedure as pleasurable as Tat did. In fact, I sought to avoid a repeat performance – ever. I had to be quite vigilant, though, for whenever Lapsi noticed anyone’s cranial cavities within her reach, she’d whip out her elongated oral appendage, faster than the eye could follow; and she’d be busily and deeply scrubbing away before her patient knew what was happening.

This canine ear-eye-and-nose cleaner masterfully worked her tongue like a wet, high-speed drill, reminiscent of the one in my dentist’s office – and I speak from experience with both tools. When Lapsi caught me off-guard and started scouring my ear, I feared she’d bore a hole all the way through my brain. The procedure tickled so much that I was practically helpless to stop her, and my efforts to dislodge her while I was weak with laughter only encouraged her to bore faster and farther. Lapsi also cheerfully tried to wash any available nostrils, canine or human, thereby providing the patient with the added sensations of gagging and suffocating.

From puppyhood through old age, Lapsi kept our other dogs’ ears so clean that they had no ear infections throughout the years she was with us. So, while I’m pouring ear cleaner into pugs’ ears, I often reminisce about how Lapsi did a better job of cleaning ears –and how she got a lot more pleasure from doing it than I ever have.

Some of Lapsi’s “patients” are shown below.

20-4 tish, tat, laps, M&B           20-5 Penny & Lapsi       20-7 Lucy

 20-8 Scotty   20-9 Rosebud   20-6 Bozo


Pugs’ Ears

Pugs have a number of different “styles” of outer ears (ear flaps), or pinnae. Take a look at the pinnae in the photos below.

19-01 Charlie ears Photo of our Charlie


19-02 pug2  Photo from


19-03 pug3Photo from×800.jpg


19-04 pug4    Photo from–1197386145.jpg


19-05 pug5  Photo from:

Whatever way they flop, pugs’ pinnae are near the top of the head (probably because there’s no room for them anywhere else). These cute little flaps cover the openings to the ear canals, which direct sound waves down to the eardrums.

The undersides of the pinnae should be kept clean, as in the photo below.


If the inside of an ear flap is red or inflamed, the pug may have an external ear infection (otitis externa) that probably warrants a visit to the veterinarian. Regular cleanings help you spot such an infection before it gets as bad as the one below.

19-07 Otitis externa    Photo from

However, it’s not sufficient just to clean the pinnae. It’s important to pour ear cleaning solution into the ear canal (as in the photo below), squish it around, and then soak it up (I use a rolled-up piece of cotton to do this). There’s an excellent article on how to clean pugs’ ears at

19-09 cleaning ear Photo from

I clean our pugs’ ears religiously – every Sunday, in fact. Weekly ear cleanings usually are needed to prevent pugs’ ear infections, or at least to minimize the number and intensity of such infections. This schedule also forces me to examine the undersides of our pugs’ pinnae, so I’m more likely to catch an external ear infection before it gets very painful.

But why are pugs so prone to ear infections? Would you believe that it’s because of that smushed-in snout? Think again of how the pug’s snout and all its anatomical components are shoved back, toward the skull. An earlier post, Beautiful, Beguiling, Bulging Eyeballs (January 25, 2016), explained how there are not quite enough “parking spaces” available for the anatomical components that belong inside a pug’s head; that includes the ear canals. The canals of a non-pug dog are shown below.

19-08 non-pug ear canal

Diagram from

Unfortunately, with a pug, the squished snout takes up a lot of head space.Therefore, a pug’s ear canals may not be as straight as this diagram depicts. The canals may have to wend – or wind – their way along a narrow, twisted route to find paths through any leftover space in the pug’s head. Thus, a pug’s ear canals are likely to be narrower and more crooked than those of a dog with a snout that extends forward, outside the main part of the skull.

So, with those floppy flaps blocking the entrances to the ears, and with the ear canals being circuitous or narrowed, it’s unlikely that a pug’s ears can get adequate ventilation; thus, moisture accumulates easily. Such conditions are akin to broadcasting an invitation for bacteria and yeast to move in, set up housekeeping, and raise large families in the pug’s ears. Therefore, it behooves the landlord (i.e., the pug’s human) to keep the premises as clean as possible, in the hope that doing so will cause the nasty interlopers to seek living quarters elsewhere, and not settle in the pug’s ears.

Our pugs are not quite as blasé about ear cleanings and ear medications as they are about eye meds, but they do keep themselves quiet and still during these ministrations. I think that’s because they know they’ll get a special jackpot-size serving of one of their favorite dog treats afterward. (I don’t know whether this is positive reinforcement or bribery; but whatever it is, it works for me.)

19-10 Sam, Charlie, Sarah lightThese three pugs wait for their after – ear-cleaning treats.

More About Pugs’ Eyes

You may recall that the original breeders of the pug wanted a dog with large, front-facing eyes, like a human infant’s (see How Did Pugs Lose Their Snouts? Posted October 27, 2015). In the same tradition, today’s dog show judges and pug breeders put a high value on eyes that are “very large, bold, and prominent.” Without a doubt, without a snout to detract from them, our own pugs’ eyes look very large and prominent, indeed.

Here’s Sarah (below), her “very large” and “prominent” eyes bulging a bit more than usual, as she waits for a treat.

0-Xylitol Oct 4


Pugs’ eyes also appear to be “bold.” Pugs are helped along in this by the fact that their eyes are encircled by dark pigment that has the appearance of eyeliner. Like eyeliner make-up for humans, this pigment emphasizes the eyes. This natural eyeliner is worn by all pugs, but it’s more visible on fawn pugs like Sarah (below).

Sarah cuddle bed crop


On a black pug, black eyeliner just isn’t very noticeable.  Below, even though Duchess has gotten very gray, you can still see the “eyeliner” on her lower eyelid.

Ch1-03 Duchess

Those big, bold bug eyes may be just what pug breeders and dog show judges look for, but a pug’s eyes are sitting targets for all kinds of loose fluff and stuff blowing in the wind, such as pollen, dirt, or other debris, as well as any pug-level swishing weed or vine. The assault by such foreign matter irritates the outer covering of the eye, and then the irritated area provides a great place for germs to enter and multiply.

Because of such assaults on their eyes, our pugs have learned that daily applications of various medicinal eye drops and ointments area normal part of life. In fact, Sarah even voluntarily tilts her head from one side to the other, making it easier for me to apply the drops to each eye.

Sarah eye drops crop

Sarah does this so blithely and automatically that you’d almost think that this, too, is a trait that pugs are born with – but she’s the only pug who helps me out this way.

Cleaning a Pug’s Nasal Fold (or “Nose Roll”)

Today, I’ll give step-by-step instructions on how to clean a pug’s nasal fold, or as it’s sometimes called, a nose roll. This area must be cleaned regularly, all the way down to the bottom, where it’s dark and damp – just what bacteria and yeast look for when they peruse the real estate ads for a place to raise their families. If those nasty bugs move in, they do not make good tenants: They can do a lot of damage to their living quarters, and can cause nasty skin infections.

In last week’s post (Feb. 1, 2016) I wrote about Sarah’s having most of her nasal fold surgically removed, along with her errant eyelashes, because of damage to her eyes. Although her nasal fold is nearly gone – along with a large chunk of change for her surgery – I still must clean the valleys from which her mountainous fold was excavated; these valleys remain a haven for germs. Because Sarah doesn’t have a real nasal fold to show you, Charlie (below), a former foster dog from Pug Rescue of North Carolina, will model how the cleaning is done.

17-1 Charlie model

Before you start, choose the item you’ll use for cleaning, and have it handy. A number of things can be used, e.g., cotton balls, cotton-tipped swabs, a thin washcloth (laundered daily), or unscented baby wipes (perfumes may irritate the dog). Dog eye wipes also work; they’re safe for the skin, and handy if you’re cleaning the dog’s eyes at the same time, but they’re the most expensive option. I often use white cotton gloves because I wear these at night, so old (laundered) ones are always available. Some suitable items are shown here:

17-2 cleaning supplies

The process for cleaning the nasal fold (or, in our pug Sarah’s case, the valleys left after its surgical excavation) has three steps:

  1. Examine the nasal fold, all the way down to the bottom.
  2. Clean the area with wet material until the material comes back clean after wiping.
  3. Finally, dry the area.

Let’s look at each step:

To examine the nasal fold, spread it apart with your fingers so you can see the bottom. Look at it and sniff it. If the skin is red, raw, or swollen, or if it smells bad, it may be infected; call your veterinarian if you’re unsure. If it gets worse or is not getting better in a day or so, a call to the vet definitely is in order; sometimes an antibiotic is needed.

Charlie cooperates when I examine his nasal fold (below), but you may need to use two fingers, or have someone available to hold the pug’s head the first time you do this.

17-3 Charlie nasal fold light


To clean the area: If using a cloth, wet it with warm water and wrap part of it over your finger. Do not use alcohol; it may sting the dog’s sensitive nose, and it dries out the area too much.

Below, I wrap a thin, wet washcloth around my finger.

17-4 finger in cloth


Then I wipe the bottom of Charlie’s nasal fold from one side to the other (below). Charlie seems to enjoy this.

17-5 Charlie cleaning


If the cleaning item comes up dirty  (and it may be even dirtier than the cloth below), repeat the process with a clean section of the wet cloth.

17-6 Dirty washcloth crop


Continue the process until the cloth comes back clean (below).

17-7 clean washcloth crop


Then, gently wipe the area dry, e.g., with a dry part of the washcloth (as I do below) or a fresh cotton ball. Leaving the area damp invites germs or yeast to move in and multiply.

17-8 dry Charlie

I clean our pugs’ nasal folds daily, usually after breakfast, when their faces are messy anyway. It’s amazing how much gunk can gather in 24 hours!

If a pug rubs his face against walls, carpeting, or anything else, he may be signalling that his nasal fold needs cleaning. When we first brought Sarah home, she alerted us to this need: She smeared brown goop from her nasal fold onto the corners of the walls – and then she happily licked off the offensive substance. (Food hog that she is, she probably was disappointed when I started cleaning the stuff off her nasal fold before she could rub it onto the walls and snack on it.)

Nasal fold cleaning also is part of the care for our foster pugs. Two foster pugs and two Harrington pugs are shown below.

17-9 Maija & 4 pugs

The Pug’s Hallowed Nasal Fold

I learned first hand – or second, if you count our pug Sarah as being first – that the “beautiful, beguiling, bulging eyeballs” (see my January 25, 2016 blog) are at the mercy of a pug’s nasal fold (also called a nose roll). This is a section of skin that wraps around the top and sides of a pug’s nose, just below the eyes. The nasal fold originates from the skin that once covered the long-ago, long-gone long snout that was bred out of the pug breed.

16-1 Pug nasal fold

This adult pug has a normal-sized nasal fold.

Photo from

A large nasal fold is prized by dog show judges. Our Sarah, a dog-show dropout, was born with a nasal fold of wondrous proportions. Unfortunately, a large nasal fold is not such a prize from a pug’s point of view. In fact, it can have a devastating impact on a pug’s ability to see. It’s not that the pug can’t see over the nasal fold – although I suppose that might be possible with some pugs.


This young pug has a large nasal fold.

photo from


16-3 adult large nasal fold

This adult pug has a very large nasal fold.

Photo from

What a big nasal fold definitely may do, because of its size and weight, is to exert pressure on the lower eyelids. This can worsen an existing enropion, a genetic condition where the bottom lids roll inward, toward the eyes.


This is the right eye of a pug. The entropion, a lower lid that folds in toward the eye, is at the bottom of the eyeball, toward the pug’s nose. This particular entropion comprises about 1/4 of the bottom eyelid.  (This text is mine. Maija)

Entropion of the lower lid that has caused a corneal ulcer (as shown with fluorescein dye staining)  Photo and this caption are from:

An entropion can be especially serious when some of the bottom eyelashes already assert their individuality, as Sarah’s did, by growing toward the eye instead of away from it. These errant eyelashes, called distichiae, grow from the inner aspect of the eyelid, behind the normal eyelashes.

16-5 distichia

This photo shows several distichiae, growing toward the eyeball.

Photo from

 In Sarah’s case, the pressure from her impressive nasal fold caused those pesky lower eyelashes to scratch the cornea, the clear covering that protects the iris and the pupil. As a result, by 16 months of age, her corneas already were scarred; unchecked, the scarring could have progressed to blindness. Fortunately, a veterinary ophthalmologist, or animal eye doctor, stopped the progression in its tracks by removing those prickly bottom lashes – along with most of that hallowed nasal fold.

16-6 S&H on couch

Note the nearly absent nasal fold on Sarah (left) vs. the intact nasal fold on Harley (right). Only the areas affecting Sarah’s eyes were removed; what remains is on top of her nose.

Although we joke that our female pug had to have a facelift before she was 18 months old, the surgery did produce the desired result; over 12 years later, Sarah can still see.

But that’s not all: More about the nasal fold next week….