There was a time when changing the appearance of a woman in a photograph would take hours and hours of expert, painstaking work by hand. Techniques in the darkroom allowed 20th-century photo editors to “dodge” or “burn”: over- or under-expose images in order to remove “flaws”, such as fine lines or rippling pockets of fat. Retouching required specialist equipment – paints, gelatine, brushes.

Towards the end of the century, Photoshop transformed the way image manipulation was conducted, but nonetheless it still required time and skill from trained professionals, and the software was expensive.

Now, thanks to the rapid rate at which software has developed, anyone can retouch a photograph of themselves in a matter of seconds. Powerful phone apps have, to an extent, democratised photography, in that people can experiment creatively with the images they produce without forking out money for expensive equipment or spending hours hunched over a magnifier. The history of the medium tells us that photographic images have been doctored since its very inception. It is nothing new. But still, there is a dark side to the way retouching is used, especially when it’s on women’s bodies.

At a recent barbecue, a friend showed me how you can doctor your Instagram photos using an app. At the touch of a button, she smoothed skin and slimmed limbs, adjusted contrast and lighting, airbrushed out “imperfections”.

This girl, by the way, is sensationally beautiful: the kind of girl men follow around rooms like cartoon dogs drooling over a dangled pork chop. And yet she airbrushes herself.

The debate surrounding the west’s skewed, stereotyped female body ideals trundles on, as it always has. In Britain the Women’s Equality party, in collaboration with the models Rosie Nelson and Jada Sezer, is taking the fashion industry to task over its continuing fetishisation of underweight, prepubescent figures. Their work is to be applauded. But this is about so much more than the fashion industry now.

Retouching and airbrushing are rife not just among the glossy pages of magazines but also on social media platforms such as Instagram – platforms that make claims of veracity and authenticity despite attempts by teenagers such as Essena O’Neill to reveal the truth behind the images.

Some phones now even do the work for you. In June, Instagram user Mel Wells blasted Samsung for automatically doctoring her selfies using its “beauty” setting. Forget the glamorous magazine offices of New York, Paris and London for a moment. Images of female perfection are being created by teenagers in the front room.

Last year the psychiatrist Dr Pippa Hugo warned that photo retouching by teenage girls was becoming the new normal. As many as nine out of 10 teenage girls in some schools would doctor themselves to appear thinner, she claimed – with disturbing psychological consequences.

Isabelle Whiteley, a photographer and researcher, has been travelling up and down the country interviewing girls between the ages of 13 and 18 for her project That’s What She Said. This is an endeavour that uses the girls’ own experiences to try to counteract damaging media narratives. It confirmed the prevalence of photo editing and doctoring among teenage girls.

“It would be more unusual for them to upload a completely undoctored picture to Instagram”, she told me, describing the practice as an “open secret”. Everyone does it, in other words, but no one admits to it.

The result is huge damage to the confidence of young women. Because now, not only are they comparing themselves with the models and actresses in magazines and on their screens, but with their peers – and, perhaps most distressingly, with themselves.

You create an online alter ego for yourself, and she is gorgeous and sexy and perfect, and what you think boys want. She adheres to whatever archetype is popular among your friendship group, school, class demographic – whether it’s the skinny supermodels of high fashion or the pneumatic, waist-trained hourglasses of the Kardashian clan. But then you see yourself in the mirror, and it’s just not good enough.

Whiteley tells me the competitiveness, jealousy and bullying among girls interacting with one another online are out of control. Study after study shows that social media is harming the mental health of teenagers.

Some who grew up in a different time will dismiss this issue as pure and simple narcissism, but such an analysis fails to grasp the psychological complexities of the problem. Those of us who know what it is like to grow up in a culture with a value system that places your body above all else will know just how much energy this preoccupation expends – how it bleeds away at your ability to act in the real world, to achieve things.

Of course there is an element of narcissism in selfie culture, even if it is one largely rooted in insecurity – where the likes and the compliments appear to add value to your existence as a young woman in a society obsessed with female bodily perfection. Humans have always been narcissists – they just didn’t have the technology to facilitate it. And everyone else wasn’t doing it too, egging you on, making you feel worthless if you didn’t participate.

Now it is worse than ever. These girls sit on their devices, entranced by a universe in which they feel as though they matter, and they are increasingly unreachable. There’s a meme going around called Me at 14, which highlights the widening gulf between even my generation – the first to live out our teens online, but still victims of the traditional photographic evidence of gawky awkwardness and poor fashion choices – and theirs, with their pouting, pornified poses, contouring and poreless skin.

In 2016 we’re beyond needing to teach girls about the artifice behind image manipulation. They know very well. But that doesn’t mean that they are immune to its effects, that they don’t desperately feel the need to change themselves as they compare their young bodies to those of supermodels.

Many put Victoria’s Secret models as their phone backgrounds as “thinspiration”. Whiteley tells me one teenage girl described the annual Victoria’s Secret fashion show as “hell every year” because of the impact of the coverage and social media discussion on her self-esteem.

I don’t know what the answer is. But I do know that this is a toxic development in the adolescent experience of young women. It’s unbelievably easy to doctor a photo. I do it to a photo of myself taken in the garden last month, and in under five minutes I am slimmer, browner, better.

I wouldn’t be a product of my environment if I didn’t think the “after” image trumped the “before”. The difference is, I would never post it claiming to truth; lots of younger girls would.

That daughter, sister, friend or niece of yours could be sitting over there in the corner on her phone cutting bits off herself with the precision of a surgeon, ruthlessly assessing her flaws with an eye more critical than the most selective model booker in New York City. And you’d never know.