In the 50s it was epitomised by curvy, pouty Marilyn Monroe.
By the 70s it was all flares and hair flicks - thank you Abba and Charlie's Angels.
And if you were to look back to the 80s and could see over the shoulder pads you'd spot the smiley, bouncy, big-haired beach girl look epitomised by Christie Brinkley and Cindy Crawford.
So what will we see when, years from now, we look back on the current generation?
Yep, when archaeologists disinter Instagram, which will be as retro as the Box Brownie by 2050, they'll find billions of pictures of women looking like porn stars.
Dull-eyed, mouth slightly parted, chin tilted back and lips as plumped as a whoopee cushion, they look as empowered and appealing as a blow-up doll.
Everyone from Jennifer Lopez and Elizabeth Hurley to Rita Ora, the Kardashians and Chloe Lattanzi have adopted the face pose, which effectively makes them look like they're trying to simulate an orgasm having taken a handful of Valium.
Grown women are entitled to do what they like with their faces but when the disempowered "I am a sex object" pose filters down to tweens and teenagers it's essential we call it out.
As columnist Sarah Vine, writing in the Daily Mail, points out: "Pornography has already corrupted the normal perception of women's bodies. Now, it has extended its toxic aesthetic to our facial features."
It's time we brought back the smile.
At the risk of sounding like my own nana, it's as if we've forgotten that a warm, natural, expression of happiness not only makes you feel good but infects everyone around you with joy.
To look at Snapchat and Instagram you'd think a whole generation of girls were failing to enjoy their lives. From Victoria Beckham to catwalk models to the photographs now uploaded online after every teenage party it seems girls have given up on smiling.
I've noticed my own 13-year-old daughter doing it. She'll be larking around, dancing, making a smoothie, swimming, playing with the cat and it's all laughter and smiles. But if a friend takes a picture or a group of them start taking selfies, out comes the pout.
I can see why women do it. Adopting a passive porn face highlights the cheekbones, plumps the lips and rids the face of the wrinkles round the eyes that typically accompany a smile. Throw in a bit of extra eyeliner via Photoshopping and add a filter and, sure, you'll look younger and sexier.
But do these women - and, increasingly, girls - want these pictures as a record of their lives?
Porn face is not empowering. It doesn't say "I own my life". Rather, it's the miserable manifestation of a world obsessed with what it looks like rather than a world intent on living.
I want to see women smiling - on the red carpet, in advertising campaigns and on the catwalk. I'm fed up with "haughty couture" and the disdainful expressions grown women are forced to adopt as if a warm grin might ruin the look of the garments. Clothes are fabulous accessories to life - why aren't designers insisting their models express as much?
From now on I'm employing a new "like" policy. I'll buy clothes from retailers where the women modelling them look happy to be alive. Likewise, social media. Anyone smiling gets a "like".
Anyone hiking, swimming, cooking, sailing, rock-climbing, dancing - in fact doing anything with their bodies other than just photographing them also gets the thumbs up.
And the porn faces? I'm blocking them.