The science of smiling

Smiling is the most studied facial expression there is, and one of the most over-claimed. Plenty of what circulates online - exact muscle counts, precise happiness percentages - is repeated far more often than it is checked.

Here is a fair summary: what is well established, what got knocked down in the replication crisis, and what remains genuinely useful.

Well established

• There is a real difference between a genuine smile and a polite one. The genuine version, named after the 19th-century physiologist Duchenne de Boulogne, involves the muscles around the eyes as well as the mouth.
• Most people can tell the two apart, even if they cannot say how.
• Smiling is contagious - people tend to mirror expressions automatically.
• Babies smile socially from around six to eight weeks old.
• Smiling changes how others treat you: smiling faces are generally rated as more trustworthy and approachable.

The bit that got complicated

• The facial feedback hypothesis says that making the expression can nudge the feeling.
• A famous 1988 study had people hold a pen in their teeth, forcing a smile shape, and found they rated cartoons as funnier.
• A large multi-lab replication in 2016 failed to reproduce it, which became one of the well-known cases in psychology's replication crisis.
• A bigger coordinated study published in 2022 found a small effect after all, under some conditions.
• Fair conclusion: smiling may give a small nudge to mood. It is not a treatment for anything.

Claims to be sceptical of

• Exact muscle counts for smiling versus frowning - the numbers vary by source and by how you count.
• Precise figures for how many times a day children smile compared with adults.
• 'A smile burns X calories' - not a meaningful measurement.
• Anything promising a specific percentage increase in happiness.

What is genuinely useful

• A real smile is worth more than a forced one, and people can tell.
• Smiling first tends to get one back - the cheapest social move available.
• Being smiled at by a stranger measurably improves how people rate a brief interaction.
• If you cannot manage a smile on a hard day, that is not a failure of willpower.

Browse gifts to make someone smile

How to write it so it lands

• Be wary of any smiling statistic quoted to the decimal point. Most trace back to nothing.
• The social effect is the reliable one: smile first and you usually get one back.

Where to shop next

• Why laughter matters
• The science of smiling
• A short history of British comedy
• Best British sitcom one-liners
• Feel good days of the year
• World Smile Day
• International Day of Happiness
• April Fools' Day
• Random acts of kindness ideas
• Gifts to make someone smile
• Planning the party? Birthday party ideas
• How to make a balloon arch
• Photo booth prop ideas
• All guides

Frequently asked questions

Does smiling actually make you happier?

Possibly, a little. The famous 1988 pen study failed to replicate in 2016, though a large 2022 multi-lab study found a small effect. Treat it as a nudge, not a cure.

What is a Duchenne smile?

A genuine smile that involves the muscles around the eyes as well as the mouth, named after the physiologist who first described the difference in the 1800s.