Can Dogs Lose Their Ability to Smell?

hound dog — A dog's sense of smell is one of its most important. Can they lose it as they age? MICHAEL LOFENFELD Photography/Getty Images

When you take your dog for a walk, you know you're going to stop at every bush, fire hydrant, mailbox and any other "marked" item along the route. And that's because dogs have highly sensitive sniffers. Their noses are constantly processing information left by other neighborhood dogs or critters that have passed through their turf with their amazing noses.

Scientists say a dogs' sense of smell is 10,000 to 100,000 times more acute than humans. Dogs have been trained to sniff for bombs at airports, to participate in search and rescue, and to even detect certain diseases, like diabetes and possibly coronavirus. But just like any other of the senses including sight, hearing or taste, that sense of smell can disappear for a whole host of reasons. If it does, it can be confusing for the dog and challenging to diagnose.

Anosmia in Dogs

Anosmia — the loss or the decreased ability to smell — is a fairly common symptom that people experience with illness or trauma. We heard about it most recently during the COVID-19 pandemic. When it happens, people usually self-report it. Unfortunately, dogs can't tell their people what's going on. Instead, they may pick at their food or behave strangely.

"When we diagnose or document anosmia in a dog, we're doing it based on changes in behavior patterns or things they used to do that they can't do anymore," says Dr. Sarah Moore, a veterinarian and professor in the College of Veterinary Medicine at The Ohio State University. Moore also specializes in veterinary neurology and neurosurgery. She says it takes a very astute owner to pick up anosmia in dogs.

"It's quite hard, especially if it's just one side of the nose," she says. "If they can still smell out of the other it can be really difficult for the owner to realize there's something wrong."

Moore says owners typically bring dogs in when it's affected their work — doe example, a police dog doing scent work or dogs at the airport sniffing for drugs. She had a case of anosmia in a dog that was a bedbug sniffer.

"The dog went to people's houses and smelled out bedbugs and the owners noticed a change in the way he did his job," she says. "That often triggers the visit to the vet and by then it's usually a complete loss of smell because those dogs are so good at compensating for any loss of smell."

Why Do Dogs Lose Their Sense of Smell?

But what causes anosmia? Is it caused by age, disease, trauma?

"The list of concerns is going to include things like infections of the lining of the nose or chemical irritants, things that can cause inflammation of the nose lining, whether that be infectious or otherwise," she says. "Also, problems of the brain can actually cause issues with smell."

The link between a dog's nose and its brain is nothing short of astonishing. The canine nasal cavity (or olfactory lobe) is positioned directly behind the nose itself. It is lined with all kinds of tiny nerve cells that connect directly to the brain. Dogs have up to 300 million olfactory (also called odorant or smell) receptors depending on the breed compared to about 6 million in humans.

"In dogs, the olfactory lobe is massive," says Moore. "If you were to look at a dog's olfactory lobe compared to a human, it's huge in a dog. It's because their sense of smell is so highly developed. Problems in that area of the brain can cause altered smell. So, tumors of the brain, strokes, head trauma, injury can all impact the sense of smell."

Can It Be Treated?

However, once the veterinarian knows what is causing the anosmia, it can usually be treated. A sinus infection caused by bacteria is typically treated with antibiotics. If the problem is brain-related, such a tumor, surgery may be an option, or they can try radiation therapy.

Loss of smell is temporary when caused by an allergic reaction to medication or exposure to chemicals or other irritants and will usually wear off with time, though some loss of smell may linger. However, viral infections that cause loss of smell could become permanent, depending on which virus is causing it.

Moore says questions about the link between aging and anosmia in dogs are fair because there's some evidence that the condition is linked with aging in people, though she has yet to see studies done linking the condition in dogs.

For dogs with viral infections or those that can't otherwise be treated, the good news is that if it's just a loss of smell, the dogs usually do pretty well with their lot in life.

"However, if they have a job that requires smell, they may have to change their line of work," says Moore.

For pups with brain tumors or other brain related issues, the result is more complicated and unfortunately, less cheery.

"The problem with brain tumors is that they do get worse and tend to grow and cause other problems eventually," Moore says. "There is some palliative care we can provide, sometimes we can use steroids to help with inflammation around the tumor, and that can be helpful for a period of time but it's not a permanent fix. From a quality of life standpoint, if they're having a lot of other problems, owners might need to consider putting their dog to sleep."

Moore says that is definitely a worst-case scenario and that in the vast majority of dogs, anosmia is a condition that will not limit a dog's quality of life.

"While it might cause a change in the dog's behavior," she says, "The good news is that the most common cause of loss of smell in dogs is related to sinus infection so most of those are going to be treatable problems."

Now That's Interesting

One reason dogs smell better than humans is because their noses are simply built better for the job. In addition to more olfactory receptors, dog's noses are constructed to function differently. When canines inhale, a fold of tissue inside the nostril separates the airflow into two paths – one for olfaction and one for respiration. About 15 percent of the air is sent to the olfactory area as it is examined, recognized (or not) and sorted, before it is exhaled.