A new app is promising to help create perfect selfies, with simple photo-editing software that lets snap-happy users appear up to 15 pounds slimmer in their photos.

The designers of SkinneePix say the app "helps you edit your selfies to look 5, 10 or 15 lbs skinnier in two quick clicks on your iPhone."

"SkinneePix makes your photos look good and helps you feel good. It's not complicated. No one needs to know. It's our little secret", it adds.

But the app, which promises to "makes your pictures look thinner", has come in for criticism from bloggers and social media users for capitalising on people's insecurities and low self-esteem.

Designers Robin Phillips and partner Susan Green, from the company Pretty Smart Women in Phoenix, Arizona, say their app is a vast improvement on what they call "fun house mirror" apps – rival selfie-editing apps that alter the face and body. "Nothing was realistic and would just slim you down", Phillips said.

Susan Green told the LA Times she uses the "playful" app as motivation to lose weight. "It's not that I don't like how I look, I just need to be healthy. And this is how I want to try to do it."

The app is now in the Apple App Store and an Android version is in the works.

The app can only edit a single person in a shot. So glamming up for Oscar style group selfies or at sporting victories will not be possible.

The reaction of reviewers has been broadly positive. One user posted: "I love how this app makes my face look slimmer. Great for selfies. Kind of like having a good face day."

But others have been less impressed by the app. Guardian reporter Elena Cresci tried the app, and said: "Rather than looking like the healthy 24-year-old I am, I look gaunt, tired and in need of a slap-up meal. Or five. My cheekbones jut out in disturbing spikes, my ears suddenly look huge compared to the rest of me – and let's not get started on my gigantic forehead.

"That's not a look that is healthy or attractive, and certainly shouldn't be desirable. The closest I've ever come to looking like this before was after a severe bout of tonsillitis." Her male colleague said the app made him look "like a skull".

Other websites said SkinneePix was "the equivalent of sucking in your tummy" and criticised it for "perpetuating the idea that thin is better".