Technology firms have been warned to consider the impact of such apps on vulnerable people.
Body-editing apps advertised on social media platforms TikTok and Instagram are “triggering” young people with eating disorders, campaigners fear.
Adverts show how the apps can be used to alter body parts, including making waists slimmer and adding muscles.
Eating disorder charities have said technology firms should consider the impact on vulnerable people.
The platforms said the apps did not break advertising guidance, but TikTok added it does reviews its policies.
It said it is “continually looking to enhance” its framework to “support a body-positive environment”.
The social media platform, popular with teenagers, banned adverts for fasting apps and weight loss supplements last year.
Social media companies need to be held to account and “stop this unhealthy and unhelpful messaging,” said eating disorder campaigner Hope Virgo.
“Over the last year, we have seen a huge increase in the number of people with eating disorders, and while eating disorders aren’t necessarily caused by bad body image, we know there are some intrinsic links.
“The fact that Instagram and TikTok are currently advertising body-changing apps will fuel this epidemic of eating disorders further.”
Eating disorder charity Seed said it has seen a 68% rise in children and teenagers aged between 10 and 19 seeking support since the pandemic.
Danae Mercer is a health journalist with a history of disordered eating.
She regularly posts about body positivity on Instagram and Tiktok, filming “behind the curtain” videos of how bodies are edited.
“I know from my own experience, these apps can be triggering,” she told the BBC.
“The apps make me thinner and curvier than my body, even if I trained all the time, could ever be. They eliminate my pores in a way that’s not even possible in nature. They create a ‘me’ that is, quite simply, unachievable – and they do it all with a click of a button.
“The impact of technology like this is immense, and honestly I don’t think we’ll see the full result of it for years”
She said it was concerning these apps were being “targeted at particularly vulnerable teens.”
“Teens and young girls don’t understand these things yet, not fully. In the same way, we wouldn’t allow weight loss products to be marketed at children, we need to really push for new regulation around what apps are allowed to target vulnerable audiences. Especially when those apps edit bodies.”
There are several free apps available on both Apple and Android app stores that allow for convincing body enhancements.
Users can edit photos or videos, changing the size and shape of bodies and faces, smoothing skin and enhancing muscles.
“We are spending more time on these platforms than ever,” said Gemma Oaten, manager of Seed.
“As we get back to normal life, we won’t be able to hide behind screens or apps.
“People are being offered ways to distort their image online but that puts pressure on them in the real world.”
Social media companies should accept a “duty of care” and signpost any adverts which could be detrimental to body image, she added.
Beat, a UK eating disorder charity, said “body-changing apps that encourage the stigmatisation of weight, or promote the idealisation of thinness, could cause distress for people suffering from an eating disorder or vulnerable to one”.
Its director of external affairs, Tom Quinn, said: “We urge the makers of these apps to consider the impact their portrayals have on vulnerable people.
“We would also encourage anyone struggling to report triggering content wherever possible, but also consider taking a step away and instead focusing on other positive sources of support like Beat.”