Experts are concerned that the app, which puts a filter over a photo of your face to transform you into an old person, can access and store photos from your camera roll.
The free app, was developed in Russian in 2017, has gone viral over the past couple of weeks.
It also lets users swap genders, look younger and change hair colour.
But experts are now saying they are concerned over a questionable clause in the app, which can get hold of other photos from your camera roll and store them, without your permission.
James Whatley, a strategist from Digitas. UK, posted part of the clause on Twitter.
It says: 'You grant FaceApp a perpetual, irrevocable... royalty-free... license to use, adapt, publish, distribute your user content... in all media formats... when you post or otherwise share.'
FaceApp is allowed to use your name, username 'or any likeness provided' in any media format without compensation and you won't have any ability to take it down or complain about it.
ed the keys to others.'
Even when the app is deleted, it will apparently still store your images.