Cosmetic adverts featuring airbrushed images of actress Julia Roberts and model Christy Turlington have been banned by the advertising watchdog.
Liberal Democrat MP Jo Swinson complained that the L'Oreal adverts were "not representative of the results the products could achieve".
The Advertising Standards Authority agreed that the images were exaggerated and breached its code of conduct.
L'Oreal admitted retouching but denied that the two adverts were misleading.
Ms Swinson said that while some retouching may be acceptable, the adverts were "particularly bad examples of misleading advertising" and could contribute to body image problems.
"We should have some honesty in advertising and that's exactly what the ASA is there to do. I'm delighted they've upheld these complaints," she said.
"There's a big picture here which is half of young women between 16 and 21 say they would consider cosmetic surgery and we've seen eating disorders more than double in the last 15 years.
"There's a problem out there with body image and confidence. The way excessive retouching has become pervasive in our society is contributing to that problem."
Guy Parker, chief executive of the Advertising Standards Authority, told the BBC that airbrushing was a "question of degree" and that advertisements could only be banned if they were misleading, harmful or offensive.
"If advertisers go too far in using airbrushing and other post-production techniques to alter the appearance of models and it's likely to mislead people, then that's wrong and we'll stop the ads," he said.
The L'Oreal images were banned, said Mr Parker, because the company was unable to show exactly how much retouching had been done to the advert - a requirement for cosmetics adverts.
"Advertisers must be able to provide appropriate material to us to demonstrate what retouching they've done in the event we question them, and they mustn't mislead," said Mr Parker.
"In this event L'Oreal didn't provide us with that evidence so we were left with no choice but to uphold the complaint."
The French cosmetics firm admitted the image of Ms Turlington - promoting an "anti-ageing" foundation - had been altered to "lighten the skin, clean up make-up, reduce dark shadows and shading around the eyes, smooth the lips and darken the eyebrows".
However, it argued it still accurately reflected the results the product could achieve.
The advert featuring Julia Roberts - also for foundation - was down to her "naturally healthy and glowing skin", said the cosmetics firm, who added that the product had taken 10 years to develop.
It added that consumer tests had been positive, showing it helped make the skin "more radiant and luminous".
The ASA last year rejected a complaint over a L'Oreal hair advert featuring Cheryl Cole, ruling the product's benefits in that case had not been exaggerated.