We’ve always heard that dogs have a much better sense of smell than us humans do. After all, there are convict-sniffing bloodhounds, bomb-sniffing dogs, drug-sniffing dogs, even cancer-sniffing dogs. Scientists have trained canines to sniff out lung, breast, ovarian, bladder, and prostate cancers in people. In one study on prostate cancer, dogs were able to detect the disease in urine samples with a 99% success rate. And it’s not just dogs that have a super sense of smell. Pigs can hunt down truffles with their snouts, honeybees can track sweet pollen with their antennae, and sharks can detect a single drop of blood in an Olympic-sized swimming pool. Elephants can track water sources from miles away, and polar bears can smell seals from 40 miles away. How can we mere humans hope to compete with all those incredible animals?

Interestingly enough, our olfactory skills are not too shabby. The human nose is actually capable of distinguishing something on the order of a trillion different scents. “The message here is that we have more sensitivity in our sense of smell than for which we give ourselves credit,” Andreas Keller, an olfactory researcher at Rockefeller University said. “We just don’t pay attention to it and don’t use it in everyday life.”

We have olfactory receptors in our noses to pick up smells, and we also have specific genes controlling these olfactory receptors. Think of it this way. Each of us has a unique fingerprint. Apparently, we also have a unique “nose print”, meaning each of us, with different combinations of olfactory receptors and their genes, experience smells slightly differently. Mutations in certain genes can totally change our smell experience.

Want an example? Why do some people think their urine smells weird after they eat asparagus, and others don’t? This has been debated for centuries. Benjamin Franklin wrote, in a 1781 letter to the Royal Academy of Brussels that “A few Stems of Asparagus eaten, shall give our Urine a disagreable Odour”. In 1931, Marcel Proust wrote in In Search of Lost Time that asparagus “transforms my chamber-pot into a flask of perfume”.  In 1985, Gabriel Garcia Marquez wrote, in Love in the Time of Cholera, “But first he enjoyed the immediate pleasure of smelling a secret garden in his urine that had been purified by lukewarm asparagus.”

When we eat asparagus, the asparagusic acid in it (found only in asparagus and nowhere else) is digested into a group of sulfur-containing compounds. As quickly as 15 minutes after eating asparagus, these chemicals can be found in urine. These are highly volatile, meaning they evaporate into the air easily. Since they evaporate easily, you can smell them quickly. But this doesn’t explain why everyone can’t smell the particular “asparagus” odor. In fact, only about 40% of you folks reading this can smell these chemicals in urine after asparagus. The other 60% wonder what we are talking about. In 2010, the genetic sequencing company 23andMe conducted a study in which they asked nearly 10,000 customers if they noticed any scent in their urine after eating asparagus, and looked for genetic similarities among those who couldn’t. This particular ability appears to stem from a single genetic mutation, a switched base-pair among a cluster of 50 different genes that code for olfactory receptors.

This is one example of how we are learning that slight differences in humans’ genetic code have an outsized impact on how individuals perceive the intensity and pleasantness of certain scents. Some more examples?

Androstenone, a compound found in men’s sweat, is perceived by some people as disgusting and intense, by others as vaguely vanilla-esque, and others smell nothing at all. It all depends on a single gene. Sixty percent of people think beets smell like dirt. They have a genetic variation in one specific olfactory receptor. There’s a smoky odor to bacon, beef jerky, and scotch. Again, a single genetic variation controls your ability to smell this.

There are plenty of things about the sense of smell we don’t understand at all. Joy and Les Milne had been happily married for ten years when one day, she noticed his lovely musk smell she’d always enjoyed had changed. He smelled yeasty, musty, unpleasant. It didn’t get better after he showered. He couldn’t smell it; neither could anyone else. She couldn’t stand the smell, and they argued about it for 10 years. Then, Les developed shakiness and was diagnosed with Parkinson’s Disease, a progressive neurodegenerative illness characterized by tremors and other motor symptoms. Another 7 years later, as he worsened, they joined a Parkinson’s Disease support group. The first night they attended, Joy was overpowered by the smell in the room. Everyone with Parkinson’s had that same smell she had noticed on Les for years! Les (a doctor) was stunned when Joy explained how the room smelled to her. They began working with Tito Kunath, a Parkinson’s researcher at University of Edinburgh. The initial experiment consisted of a t-shirt test. Joy was asked to smell t-shirts, half that had been worn by people with Parkinson’s and half worn by healthy people. Her identification of which shirts were in which group was 100% correct. Actually, there was one shirt she thought belonged to a Parkinson’s patient and the man was healthy. However, four months later, he was diagnosed with Parkinson’s! Think about it! Joy smelled Parkinson’s ten years before Les developed any symptoms. If it could be diagnosed that much earlier, perhaps more effective treatment could be developed, and outcomes could improve.

Tito Kunath’s research has identified certain specific compounds that may contribute to the smell that Joy noticed on her husband and other Parkinson’s patients. Dr Perdita Barran, Professor of Mass Spectrometry at the University of Manchester, England, is involved in identifying scent biomarkers in Parkinson’s Disease. Out of the 25,000 or so compounds commonly found on human skin, roughly 3,000 are differently regulated in people with Parkinson’s. “We are now in a position where we’ve narrowed that down to about 30 that are really, really consistently different in all people with Parkinson’s.” says Barran. She is developing a simple skin swab test (still in research stage) to diagnose Parkinson’s more easily. All of this from Joy Milne’s uncanny super-smeller ability.

What’s next? Super smellers like Joy are exceedingly rare, and trained sniffing dogs are expensive. Electronic noses, or e-noses, are a hotbed of research now. Volatile chemicals are given off in our breath, urine, stool, and skin, and sampling these is less invasive than drawing blood. eNoses, devices with an array of electronic chemical sensors and pattern-recognition systems, can identify infections, pulmonary diseases, inflammatory diseases like sarcoidosis, and many types of cancers. Research results are promising, and I think we will see practical applications soon.

Plus, I love the fact that the most popular eNose is named Cyranose! https://www.amazon.com/dp/B0F4XR19D4/ref=sspa_dk_detail_3?psc=1&pd_rd_i=B0F4XR19D4&pd_rd_w=0oX9c&content-id=amzn1.sym.8c2f9165-8e93-42a1-8313-73d3809141a2&pf_rd_p=8c2f9165-8e93-42a1-8313-73d3809141a2&pf_rd_r=KBX51S9ES4SC4CWZJWH8&pd_rd_wg=FroBM&pd_rd_r=7129567a-5a15-41b0-bb57-be7703a0679c&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw