The X-Ray augmented reality app lets you see what catalogue models look like wearing just their underwear.
Users put their iPad or smart phone over the image of the model wearing clothes and it replaces it with a picture of how their bodies really are underneath.
The app does not actually carry out an X-Ray but uses augmented reality to approximate how each person looks.
It has been a huge success and been downloaded 75,000 times in five weeks with one million impressions on Twitter.
A video by its makers Moosejaw, has been viewed 160,000 times and the U.S. clothing company firm claims it has led to a 37 per cent boost in sales.
The app only works with the Moosejaw catalogue, however, sparking a debate on technology blogs that it is little more than a cheap trick.