When you’re a fresh-faced teen experiencing the thrill of romance for the very first time, there are any number of things that could cause you to fall hopelessly in love. Maybe it’s the sparkle in someone’s eye or the smoothness of their voice. For Joy Milne, a 69-year-old retired nurse with the singsongy brogue of a Scottish Mary Berry, it was her future husband’s scent.
She was 16 when she and Les first danced together at a party, and from the moment she found herself close to him, she was smitten. He was a year older than her and had a “lovely male musk.”
The two started dating, got married and had a few kids, relishing in domestic bliss as they entered into dueling medical careers — him as a doctor, her as a nurse. Everything was peachy until about a decade in when Les started to come home smelling differently. His formerly intoxicating male musk had undergone what seemed to be a slow, but obvious transformation, morphing into a strange, sour, yeasty smell that she didn’t recognize.
At first, she thought it might be a hygiene thing — maybe he was bringing something home from the hospital. Much to his chagrin, she asked him to shower — repeatedly — hoping some suds and hot water would wash it away. But as the days turned into months, the smell didn’t budge. Instead, it intensified, so much so that Milne stopped asking him to bathe at all. It wasn’t going anywhere, it seemed — that was just “how he smelled.”
Around the same time, something shifted in Les’ personality. Once lighthearted and wickedly funny, he started to become moody, irritable and less tolerant, losing his humor and energy in the process. By the time the Milnes were in their 40s, he’d become an entirely different man than the one she fell in love with.
The night she woke up to him screaming, shaking and attacking her was the last straw. He was in the throes of a nightmare and hadn’t meant to alarm her, but it was so jarring and out-of-character that she worried he had a brain tumor. A visit to the doctor proved her wrong, but they were offered a different diagnosis instead: Les had Parkinson’s disease.
For a while, the two made it work, dealing with his slow and painful loss of mobility and independence as best they could. But when it became too much to tackle on their own, they decided to attend a Parkinson’s support group together in 2012. That’s when Milne noticed something strange. That smell — the greasy, musty, woodsy one Les couldn’t wash off — was all over the meeting. In fact, she says, the entire room reeked of it.
“When I realized that, we had a very strange conversation,” she remembers. “I drove him all the way home after that first meeting, sat him down at the table and said to him, ‘I’ve got something to tell you. Did you know that those other people in the room smell the same as you?’’’
His eyes lit up when he realized what that meant: His wife could actually smell Parkinson’s disease. And she’d picked up on it 12 years before his diagnosis.
As Milne started to flash back to her nursing career, it all started to make sense. Remembering the distinct fragrances that would waft from the rooms of her patients with Alzheimer’s and diabetes, she realized it wasn’t just Parkinson’s that had a scent, but a number of other diseases she’d come across as well. “Right,” she thought to herself. “Diseases must have a smell.”
Since then, Milne has put her extraordinarily sensitive nose to the test, quickly and correctly identifying not just Parkinson’s, but tuberculosis, cancer, diabetes and Alzheimer’s, too. She’s currently involved in a number of smell-related disease studies, but now, as the pandemic rages on, a new test of her abilities has emerged. If she can smell other diseases, might she be able to sniff out COVID, too?
If you’re a smell researcher or a real-life X-Man like Milne, that’s the hot ticket question of the year. But, as of now, no one really knows if COVID even has a scent, let alone whether someone like Milne would be able to smell it.
“I have no idea if humans can smell COVID,” says Gary Beauchamp, emeritus director and president of the Monell Chemical Senses Center. “It’s conceivable that it might be possible, but, to my knowledge, there’s not been a scientific paper published that would convince me that we can.”
Richard Doty, director of the University of Pennsylvania’s Smell and Taste Center, hasn’t seen hard evidence of COVID-sniffing, either. But, he says, that doesn’t mean it’s not possible. “Anytime a disease damages a tissue, a variety of chemical changes occur,” he says. “These changes often produce molecules called metabolites, which are byproducts of those chemical processes. Many of these metabolites remain inside the organism, but sometimes, they’re expelled from the body through lung air or other excretions. Depending on the disease and where it occurs, you may be able to smell them.”
There are a number of ways in which that could happen. In one, the virus would have to alter a person’s hormonal levels, immune system or microbial composition enough to change their aroma. In another, the virus would damage a tissue enough to putrefy it, causing certain whiffable molecules to be released as the tissue dies off. In either case, it’s not the disease itself that has a smell — it’s the byproducts of its effects on the body. These byproducts (also called “volatile organic compounds”) are most often expressed in smelly effluvia; breath, feces, urine, sweat, sebum and vaginal secretions have all been found to carry stinky metabolites of disease.
Not every illness has a sickly perfume, but there are many that are believed to emit their own distinctive aromas. Typhoid fever smells like baked bread. Yellow fever stinks of a “butcher shop.” Diabetes is fruity — almost like overripe apples — and Parkinson’s exudes a yeasty musk. Breast cancer, melanoma, preeclampsia, liver failure, kidney disease and even certain psychiatric disorders like Alzheimer’s all produce their own signature scents as well.
You don’t need a super schnoz like Milne’s to detect them, either. According to Beauchamp, humans are constantly making unconscious detections of other peoples’ disease states, and have been doing so — as a likely evolutionary adaptation — for hundreds of thousands of years. One passage in the Sushruta Samhita — a Sanskrit medical text written a thousand years before Christ — cites the “peculiar perspiration” of many diseases as an indicator of their identification, and a number of recent studies have demonstrated that humans can smell when other people are sick.
What most of us can’t do, however, is consciously recognize and differentiate the odors we sense. Milne, on the other hand, can. She has hyperosmia, a type of synesthesia that connotes a heightened acuity for smell and a lower threshold for odor, both of which are regulated by abnormally robust signaling between the nose and brain. Because of this, she can parse out Parkinson’s from preeclampsia, identifying diseases with a freaky accuracy that often surpasses that of diagnostic machines. Milne can even smell what stage an illness is in, a superpower she sees as crucial for the early detection of disease. “The sooner I can smell it, the sooner they can treat it,” she says.
Even so, smell is far from a perfect diagnostic tool. As both Beauchamp and Doty caution, the findings around disease scents are scant and highly variable, and their quality or presence can be influenced by everything from diet to stress to hygiene.
The science is particularly shaky around viral infections. Doty says he isn’t aware of a virus — let alone a super-contagious, epidemic-style one like Ebola or SARS — that has a distinct, research-backed stench. Even if there was one, he continues, there’s no guarantee that humans would be able to differentiate it from another stinky virus with similar symptoms (or between diseases caused by the same virus).
“Coronaviruses cause a number of diseases, one of which is the common cold,” he explains. “We don’t think about colds as having a particular smell, so it’s unclear whether someone could discern a mild respiratory infection from COVID-19.” Likewise, while animals like mice and dogs have reliably sniffed out certain viruses, neither Doty nor Beauchamp are aware of any humans who’ve been able to parse out one viral fragrance from another. Nope — not even Milne.
But it’s not that Milne can’t smell viruses. It’s that she won’t. Who in their right mind would? “You can’t just go around sniffing viruses like you can Parkinson’s,” she says. “They’re infectious! I’d just be breathing them into my lungs if I tried. Most viruses — especially the respiratory ones — would make me very ill.” As such, she maintains a “very strict” protocol about what she does with her nose.
Which brings us back to COVID, an illness she patently — and sanely — refuses to smell. In fact, it’s so against protocol that she won’t even humor me by guessing how it smells. “In science,” she says, “We can only tell the truth.” Well, fine!
That said, she says she’d be happy to sniff COVID if scientists gave her an inert version of the virus to play with. But, so far, no one’s come knocking with a T-shirt full of deactivated corona, and she doesn’t expect them to, either. In the U.K. where she lives, scientists are already using the relatively cheap and easy tool of mass spectrometry to identify and diagnose COVID cases. Thus, her services haven’t been needed.
Well, that rules out humans (for now, at least). But what about dogs? They can smell everything from Bronze Age human remains to orca shit floating on the water miles across the choppy water of Puget Sound, so if the virus is too risky for people to sniff, couldn’t some hardy canines step in and do the dirty work for us?
As a matter of fact, yes they can. According to Maria Goodavage, New York Times bestselling author of Doctor Dogs: How Our Best Friends Are Becoming Our Best Medicine, there are a number of studies taking place around the world that are attempting to answer that question. She hasn’t seen anything definitive so far, but the preliminary results do seem promising. “The best research is still in fairly early phases, but it seems to be showing that dogs are picking up on a scent from the virus (in urine, for instance),” she says, assuring me that the best medical detection dog facilities have ways to render the virus inert while still allowing its scent to come through. “Detecting people with the virus is going to be quite a bit trickier, but the dogs may be able to do this.”
It would make sense if they could. With over 300 million olfactory neurons packed into their wet little snouts, dogs’ noses are exquisitely sensitive organs with a sense of smell between 10,000 and 100,000 greater than ours. Highly trained dogs can smell diabetics who have low or high blood sugar, sniff out an oncoming seizure and sense if a person is about to lose consciousness. One research group has even reported that fuzzy good bois can smell emotions from sweat and saliva samples, and a mountain of research reveals that dogs are superb at detecting cancer in laboratory settings (even at early stages of cancers that are hard to detect early in any current tests, like ovarian cancer).
Dogs even do viruses: Researchers at Auburn University’s Canine Performance Sciences recently discovered that dogs can both smell and differentiate between a number of bovine viruses that cause diarrhea, herpes and influenza, respectively.
Given that track record, Goodavage says there’s no reason why they shouldn’t be able to pick up on COVID, too. “If dogs can do this with a decent degree of accuracy, it could be a game-changer,” she continues. “If enough of them become COVID detectors, they could be responsible for a great reduction in community spread of the virus. They may be stationed as screeners at places like airports, sporting events and other venues where there are large numbers of people.” If it goes well, who knows, they may even be “coming to a mall near you, helping ensure shoppers are virus-free.”
But getting goosed by a COVID canine at some sort of futuristic smell checkpoint outside Spencer’s is still a pipe dream. Researching these things takes time, and training dogs to parse out corona from the other thousands of smells vying for their attention isn’t easy. “There are a lot of confounding factors, including if someone is wearing a scent, what someone ate for lunch and the mixing of scents in a crowd,” she says. “Dogs have to learn to ignore everything but the scent they’re looking for.” (Milne, however, says she can easily pick out diseases even when she’s in a crowded area.)
Why not train humans to sniff COVID while we wait for dogs to catch up, then? If it’s possible to neutralize the virus for dogs, it’s definitely possible to neutralize it for humans. Doesn’t that mean we could be deploying COVID-sniffing X-Men squadrons to roam the streets?
Well, just as soon as we train them. “To my knowledge, there are no existing disease-sniffing programs for humans,” Doty says. “But I don’t see why there couldn’t be. If you study an odor enough to make fine distinctions between them — and you learn to really pay attention to its subtleties — then you can be trained. The more you’re exposed to odors, the more that you could become sensitive to them.”
Milne talks about this in her family, too. Her sisters, who also have hyperosmia, often joke that they could learn each other’s “olfactory libraries” if they tried (an “olfactory library” is the catalog of scents a person recognizes). As the only nurse in the family, Milne’s library is highly attuned to diseases and medical scents, but there’s no reason, she says, why she couldn’t train her sisters to smell what she can (she’s tried and they’re “definitely not interested”).
Of course, all these tidy hypothetical predictions are banking on the fact that COVID has a unique smell at all, something that, as of today, can be neither confirmed nor denied. Still, Milne is reasonably confident that she could smell it if she tried. “What’s certain here is that diseases do have specific smells,” she says. “That means there are set molecules for that disease that I could theoretically inhale.” If she trained herself to associate those molecules with COVID, then it’s possible we’d have a coronavirus-seeking human nose on our hands.
It sounds like science fiction, but, according to Beauchamp, it’s not that outlandish of a concept. “A COVID-sniffing person or task force is something people kind of laugh at,” he says. “It seems kind of hokey, but it makes good biological sense. It’s also incredibly useful. To have smell as a diagnostic tool would mean we’d have a quick and inexpensive way to detect disease, sometimes in their early stages before they progress. So, even though the reality of that is far off, I’m very up on the idea of doing it.”
The implications of an early nasal detection system could be huge for COVID, too; the earlier in its progression it’s detected, the sooner the infected person can quarantine, and the slower its spread would be in the population.
But for now, Milne says she’s happy to wait for an inert version to come her way. “I’d much rather smell the flowers in the garden,”’ she laughs. “But if I’m able to smell it, then I hope I can help.”