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 flavour, 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 favourite 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 behaviour. 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 9 January 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 flavour’… 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 realise 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 flavours – 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.”