I have never been a smoker. Even from a very young age, I’ve been actively repelled by it. I confess I did eventually try a cigarette as a drunken student, largely due to peer pressure, and ended up with a scorched larynx and a mouth that tasted like a neglected car’s exhaust, which just reaffirmed my opinions on the matter.

So it was quite surprising when, nearly two decades later, an encounter with secondhand cigarette smoke ended up easing the intense grief I was experiencing. It was May 2020 and the pandemic was well under way. We were in the heaviest lockdown and I was racked with grief. My otherwise healthy 58-year-old father had contracted the virus in March, and succumbed to it in April. My mum and dad had been young parents – they were 20 when they had me, I’m 40 now. When he died, I couldn’t be with him, or help in any way. What updates were possible were relayed to me second- and third-hand from desperately overwhelmed medical staff. When his condition deteriorated beyond all hope of recovery, I had to say goodbye to my father via WhatsApp. From my kitchen. With 20 minutes’ notice. It was, undeniably, hellish.

While I fully supported the lockdown, it deprived me of my father’s final days and also kept me from the usual methods of dealing with grief and loss. No tearful gatherings with loved ones. No relatives taking over childcare, cooking, housework, etc, to give you the essential time to grieve undisturbed. No drowning your sorrows with friends or a proper funeral.

Nonetheless, I was still a father and husband with all the associated responsibilities during a very scary time. So, for my family’s sake, I had to swallow my pain as best I could. What other option was there? Nothing and nobody seemed able to shift the headful of roiling emotions I was experiencing. However, about a month after Dad’s passing, I was walking through my suburban Cardiff neighbourhood for my daily exercise, trying and failing to churn through my bleak and weighty emotions, when I passed a nondescript front door. I caught a whiff of secondhand cigarette smoke from some unknown and unseen neighbour who’d presumably returned indoors just before I strolled by. Normally, given my established dislike of smoking, this would make me recoil. Only this time, it didn’t. Instead of repulsed, I actually felt… better?

It’s not as if my grief was suddenly switched off, but for the first time in recent memory, my thoughts about my father were infused with a degree of fondness and warmth, rather than pain and sadness. I may have even smiled to myself slightly as I continued to plod on alone.

It was weird how a whiff of a stranger’s cigarette, something I’d always deemed unpleasant, actually lifted my mood. Especially when all other efforts had comprehensively failed. So what was it about?

Using my neuroscience knowledge, I know now that a lot of it is due to how our sense of smell works and its many unusual properties. It is far more complex and powerful than we often assume and consequently plays a bigger role in our lives than we realise. For instance, smell develops in the womb, seemingly before any other senses. Babies can detect their mother’s scent via the amniotic fluid so our sense of smell allows familiarity and bonding with a parent before we’re even born.

And it’s not just in the reproductive sense: evidence suggests smell was the first sense to evolve at all. Consider the nature of the earliest life forms – tiny complex bundles of chemicals, in a complex chemical environment. That’s essentially what smell is – information relayed to your brain about the chemicals in your environment.

Primitive brains developed memory (for retaining sensory information) and emotions (for responding to it appropriately). In this way, smell actually shaped our brains. This is, admittedly, a drastic oversimplification but, still, the legacy of it in the modern human brain is there. While it’s not the sense we rely on most (that would be vision), when it comes to the human brain, smell is still very privileged.

This explains, as countless people have observed over the centuries, why certain smells so often trigger powerful, emotional memories – from the Proustian moment to Ratatouille’s ratatouille (which are essentially the same thing), to the cliché of a faint whiff of perfume that brings vivid memories of a lost love flooding back.

Some argue taste is involved, but as a sense, it is relatively weak and crude. It is smell that’s doing the heavy lifting when it comes to complex, nuanced flavours, hence we can taste very little when our nose is blocked. Taken together, this reveals how and why certain smells, however fleeting, trigger powerful memories and emotions. That’s just how our brain works.

However, this doesn’t fully explain why the smell of cigarette smoke helped me with my grief. After all, I don’t like smoking, and my father never did it, as far as I’m aware. So, what’s with this reaction?

Part of it can be pinned to the potency and tangibility of smell. Granted, I’d been constantly talking to many people online during my harrowing situation, but as a lot of them pointed out, it’s just not the same as face-to-face. It often lacks a certain something that allows our minds and brains to consider it meaningful. So, my grief-enhancing feelings of isolation continued undisturbed.

But even the best technology hasn’t been able to replicate smells yet. So, maybe this brief blast of a stranger’s nicotine cloud was enough to reassure my frazzled brain that, despite the isolation of the lockdown, there were others still out there. I wasn’t really alone. None of us were. It’s a nice thought, but still falls short of fully explaining my reaction.

With many senses, the most recent exposure to something tends to carry almost all of the weight emotionally. Seeing our romantic partner kissing someone else will obviously overrule initial pleasurable experiences we’ve had with them. We love a song so much we play it constantly, then we grow sick of it and can’t stand to hear it again. In both cases, it’s the latest experience of something which informs our reaction.

But smell is different. With smell, it’s our first, or earlier, experiences of something that has the more enduring influence on our memories and feelings. Presumably this is to do with the much bigger and more direct impact smell has on the relevant brain systems, something tempered by familiarity. Therefore, if the first time we smell something leads to a happy experience, it will probably bring up happy memories whenever we smell it, regardless of what happens in the future.

On learning this, I realised something. Before this point, I’d been advised repeatedly to “focus on the good memories” of my late father. But that’s easier said than done, because all those memories now reminded me of loss and sadness, as his passing was so recent. Could they really be described as “good” memories any more?

But here’s the thing – I grew up in a pub, in a mining valley in South Wales. My father was the landlord. It was the early 80s. So, as much as I dislike smoking, it was essentially the olfactory background of my childhood. Now it seemed the positive memories were still in my brain somewhere. My earliest interactions with Dad, the most carefree childhood moments we shared, the many fun and ridiculous antics Dad got up to in the pub we lived in (think Phoenix Nights but with Welsh accents): these treasured memories occurred with the background aroma of secondhand smoke. The same smell I’d encountered, decades later, on my grief-fuelled walk.

That olfactory encounter essentially yanked intact positive memories of my father to the forefront of my mind. It reminded me that, even though my father had died, he’d also lived. And lived well. Nothing could ever take that away, and for the first time in weeks I felt like the pall of grief I’d been surrounded by may not be a permanent thing after all. All thanks to the often-overlooked power of smell.

I still have no idea whose cigarette I smelled. But, however inadvertent, they helped pick me up when I was at my lowest. So, if you’re reading this, my tobacco-wielding friend, I’ll say something to you I’ve never said to anyone: thank you for smoking.

Emotional Ignorance: Lost and Found in the Science of Emotion by Dean Burnett (Guardian Faber) is available from guardianbookshop.com for £9.99