The app has been at the centre of a viral phenomenon over recent days, as celebrities and normal people rush to change their pictures to find out how they would look if they were old, young, or a different genre.
But it has also been hit by privacy questions as users wonder what is happening to those photos when they are edited.
Now the app has attempted to explain how it uses the images that are uploaded, and has tried to address the most prevalent fears about the app, in a statement first reported by Techcrunch.
In a series of points, it addressed each of the concerns about the way it works in turn. While it admitted that it does take the photos when they are edited, it stressed that privacy protections are in place that should stop those images being abused.
It also did not explain or address the part of its terms of service that has caused probably most consternation, in which users are asked to agree to give up the rights to any images they edit with the app.
First, it said that it does need to upload images to the cloud so that they can be edited on its servers. But it stressed that it only uploads the single photo that is chosen by users, and that other images are not taken off a person's device.
That runs contrary to a host of viral tweets and posts, which have suggested that the app hoovers up every image on a person's phone when it is opened. Third-party security experts had already suggested this isn't the case, and iPhones have protections in place that stop an app even seeing a user's images unless permission is given.
FaceApp also admitted that those photos could be saved when they are uploaded to the cloud. But it said the main reason that is done is for "performance and traffic", so that users don't have to repeatedly upload an image, and that most of them are deleted within 48 hours.
If users want to remove data manually, then it is possible to submit a request, FaceApp said. While those might not be addressed immediately because the "support team is currently overloaded", they can be requested through the mobile app by clicking through the "settings" menu, and that feature will be expanded and made easier soon.
It also stressed that most users don't log in and that user data is therefore hard to track, and committed not to "sell or share any user data with any third parties" anyway.
Finally, FaceApp acknowledged that it is developed in Russia, a fact that has led to a rash of conspiracy theories about the way the app could be gathering data or being used in more sinister ways. But that was no reason to worry, it stressed.
"Even though the core R&D team is located in Russia, the user data is not transferred to Russia," it wrote in its statement.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies