Everyone’s suddenly posting pictures of what they might look like when they’re old.

If you’re wondering how they’re doing this, it’s by using an an app called FaceApp, which is now the top trending free app in the iTunes App Store. You can download and use for free for three days.

The app’s privacy policy said it collects the pictures you upload to its service, so keep in mind that it’s keeping the selfies you take. Also be warned that one developer, Joshua Nozzi, said on Twitter that it appears the app may try to upload other pictures from your library. If you’re concerned about this, don’t give it access to your photos when it asks, just access to the camera.

Here’s how to try the filter if you want to get in on the fun:

Open the app and decline the subscription offer. Tap the camera button in the middle of the screen. Don’t give it access to your photo library, just your photos. Take a picture of yourself and tap “use” on the bottom. Choose “old,” a filter that makes you look older. Mess around, there are some other fun filters, like hipster.

Read more at usatoday.com.