Smiling can reduce stress, trick our brain into thinking we're happy, make us seem more trustworthy and boost productivity.
Or so science says.
But as I sat on the Tube the other morning and looked around, not one person was smiling. Not one. As usual, the packed northern line train was full of bodies with their heads in their phones, blankly staring into space or reading the paper.
I was one of them too, of course.
When I got off the tube to change lines, people were cramming their way onto it before I could even get off (another reason not to smile).
Then a woman in front of me got on the tube and smiled at me. I smiled back, but thought it was slightly weird.
Why is she so happy at this time of the morning?
That's sad, isn't it? That a small gesture meant to improve happiness and the happiness of those around us made me feel 'weird'.
If I knew her it would have been fine. If something funny had happened around us I would have understood perhaps. But why did she smile at me? Does there even have to be a reason?
Today is World Smile Day.
Harvey Ball, an artist from Massachusetts created the iconic smiley face image in 1963, but as years went on he was concerned the original meaning of the smile - to symbol good cheer on the planet - had become over-commercialised.
He came up with the idea of World Smile Day to devote one day a year to smiles and kind acts. Make one person smile, that's all he wanted.
Inspired by Mr Ball and that woman who smiled at me on the Tube on a weekday morning, I decided to try it. I decided to devote my commute to work to smiling at strangers and see if just one smile can really do all that good.
My goal? Five smiles in the 50-minute commute.
Smile One: To The Tube Man I See Every Morning
Every weekday, I see the same man stood by the ticket barriers at the Tube station in a bit of an early-morning daze. He mainly moans at people when they hold up queues at the barriers when their oyster isn't working.
I walked up to the barriers and sure enough, he was stood in the exact same position looking as grumpy as usual.
I smiled. He sort of smiled back. It was a bit awkward.
Smile Two: To The Man Who Offered Me A Seat
To get offered a seat on a busy morning commute is a rarity and although it might seem obvious to smile when someone does, I usually mutter "thank you" without making eye contact and sit down with my head in my book.
The man and I both headed for the empty seat at the same time. "You go," he said. I smiled, said thank you and sat down. He said "no worries", but didn't smile back.
That was better. Less awkward.
Smile Three: To The Man Offering Me Shortlist Magazine
I was feeling desperate, I was already nearly at work and walked out of the station to be greeted by another person trying to fill my bag up with free magazines and newspapers.
Most mornings, I ignore, avoid and walk on. This morning I looked up, smiled, said "no thank you". He smiled back and said "have a lovely day!".
This time it genuinely felt nice that I engaged in the shortest conversation ever, but made someone smile. I always think of those people handing out freebies and flyers as a bother, a nuisance. But as I was walking up the road to work, I actually did feel nicer because I wasn't walking along looking like the grumpiest person alive.
Smile Four: To The Woman Who Walked Into Me While On Her Phone
This is a very big pet hate of mine. LOOK WHERE YOU ARE GOING. But from the aftermath of making Mr please-take-this-free-magazine smile back at me, I actually genuinely felt in a nicer mood.
She walked towards me looking down, as I was walking ahead in a bit of a daze and we slightly bashed shoulders.
On any other morning this would piss me off. It's early, I'm on my way to work, I'm tired and right now I'm cold.
"I'm sorry!" she said. Partly being my fault I just smiled and said not to worry. She smiled back. IT WORKED. At this point I concluded smiling could be contagious. Like a yawn.
Smile Five: To The Receptionist At Work
It was my last shot as I walked into my office building. Usually? I briefly say morning and scurry up the stairs to get breakfast.
Today? I smiled, said morning and he greeted me with a similar, less-morning-like response.
I actually walked upstairs smiling and feeling genuinely a little bit warmer inside.
Smiling humanises people. Smiling made me realise all those people on my morning commute - the bodies crammed on the Tube, the people working at that time in the morning, the people you simply walk past - they're actually real people.
It's a selfless act to smile at someone. It takes hardly any effort, but I genuinely believe you can make someone's day that little bit better by wiping the blank look off your face and giving that tiny bit of an emotional connection - simply a smile.
Forcing a smile even when you don't feel like it does make you feel nice inside, even if it's just for a couple of minutes. And while it's not something I'm going to be doing every morning, I'm 100% more aware of how damn good smiling can be.
Did smiling at random people make me feel happier? Yeah, it actually did.