Nick Johnson skims the lunch menu at the White Dog Cafe, a warren of little rooms and ante-rooms in Philadelphia’s university district. “Beef empanadas… I would have loved those. But all that braised beef would just get lost on me. Fish and chips I avoid: all fried foods taste the same. I’m looking at the fish tacos. I know I’ll get the spicy heat and a little bit of pineapple flavor, and with the peppers and the guacamole, there’ll be some mouthfeel there.”
He orders the tacos, and we get a beer that’s on tap. It’s called Nugget Nectar, and it’s produced by the local craft brewery that Nick’s worked at for the past ten years. Nugget Nectar used to be his favorite beer. “It has a real nice balance of sweetness and hops. But now,” he says, and his face falls, “it’s a shell of its former self to me.” He can describe what it smells like: “piney,” “citrusy,” “grapefruity.” But he can’t smell it any more.
We don’t think of ourselves as being particularly good smellers, especially compared with other animals. But research shows that smells can have a powerful subconscious influence on human thoughts and behavior. People who can no longer smell — following an accident or illness — report a strong sense of loss, with impacts on their lives they could never have imagined. Perhaps we don’t rank smell very highly among our senses because it’s hard to appreciate what it does for us — until it’s gone.
Nick, who’s 34, can pinpoint the moment he lost his sense of smell. It was January 9, 2014. He was playing ice hockey with friends on the frozen pond at his parents’ place in Collegeville, Pennsylvania. “I’ve done it millions of times,” he says. “I was skating backwards, slowly, and I hit a rut on the ice. My feet went out from under me. I hit the back right side of my head. I was out. I came to in the ambulance, people surrounding me, blood pouring out of my ear.” He had ruptured an eardrum and fractured his skull in three places. He had blood on his brain, and was suffering from seizures. “I had no idea what was going on.”
After making a rapid recovery, he was cleared to drive again six weeks later and returned to work as regional sales manager at Tröegs brewery. Before long, he found himself in a meeting about a new beer. “We were tasting it, and the others were saying, ‘Can you smell the hops in the beer?’… and I couldn’t. Then I tasted it. There were guys saying, ‘It’s got this pale biscuity flavor’… and I couldn’t taste it. Then I went and tried one of the hoppier ones… and I couldn’t smell it. That’s when it clicked.”
The stress of the injury and all the medication perhaps explain why he didn’t realize he had lost his sense of smell sooner. It came as a shock, he says. Now, though, he is acutely aware of the effects it has had.
Losing enjoyment of food and drink is a common complaint for people who lose their sense of smell. You can taste sweet, salty, bitter, sour and umami with your tongue. More complex flavors — like grapefruit or barbecued steak — depend on smell. But for Nick, as for many people who can’t smell, there’s another category of loss altogether.
At the time of his accident, Nick’s wife was eight months pregnant with their second child. Over lunch, he says: “I joke I can’t smell my daughter’s diaper. But I can’t smell my daughter. She was up at 4 o’clock this morning. I was holding her, we were laying in bed. I know what my son smelt like as a little baby, as a young kid. Sometimes not so good, but he still had that great little kid smell to him. With her, I’ve never experienced that.”
Subtleties of Smell
Nick takes a deep sniff of his glass of Nugget Nectar, the beer that was once his favorite. Volatile chemicals from the liquid are drawn high up into his nostrils, to the roof of his nasal cavity, the part specialized for smelling. Then he takes a sip, and those same chemicals travel up from the back of his mouth to the same part of his nose. So far, so good.
Next, the molecules are absorbed into the mucus inside his nose. This is critical for something to be smelly: at the moment, no one can look at a molecule and say, based solely on its structure, how it will smell, or even whether it will smell at all. All we know is that for something to have a smell, its molecules must easily evaporate so they can be carried in air and inhaled, but they must also dissolve in mucus to be detected.
For a healthy person sniffing a beer, or their child, or a T-shirt belonging to their partner, exactly what happens next, leading to a perception of the beer or the person as a complex aromatic whole, is only hazily understood. Lurking within the mucus of the nose are the tips of olfactory receptor cells. These nerve cells lead directly to the brain. While we have millions of these cells, there seem to be only about 400 types, each of which binds to a specific molecule (the number is debated; some argue it could be closer to a mere 100). Based on the pattern of activation of the various receptor types, when I sniff Nugget Nectar, I recognize it as ‘beer’. Nick smells nothing — the impact of his fall probably damaged or even killed his olfactory nerve cells, and his brain receives no information about the smell of his drink.
Before his injury, Nick had a highly sensitive nose. Unlike me, he would have been easily able to distinguish Nugget Nectar from other beers. That ability comes with experience. After the incoming smell signal pattern is processed, this information is sent to different parts of the brain, including regions involved in memory and emotion, as well as to the cortex, where thinking takes place. We can then quickly learn to pair patterns of receptor activation with the source of the smelly molecules.
Until recently, it was thought humans could detect perhaps only 10,000 different scents. But there’s been a radical rethink, according to Joel Mainland, who’s researching the fundamentals of smell at the Monell Chemical Senses Center, a world-leading institute for research on smell and taste in Philadelphia. A recent paper in the journal Science estimated that we can detect more than a trillion smells. A few problems have been raised with the methodology of that study and there’s still a lot of debate about the true figure, but Mainland certainly thinks that we’ve underestimated our abilities.
Because of the nature of his job, Nick underwent all kinds of sensory training to improve his smell and taste. The rest of us probably have untapped potential, too. Yes, dogs are renowned for being able to track a person’s scent across a field. When Mainland was a PhD student, his supervisor suggested investigating whether humans could be trained to do the same thing. It turned out they could.
Dogs have more types of olfactory receptor than we do — but as Mainland points out, cows have more than dogs (about 1,200 compared with 800) and it’s not clear that cows are significantly better at smelling. The poor reputation of humans may be down to the fact that we spend comparatively little time actively sniffing and so training our sense. What difference would it make if we all put more effort into smelling the world around us?