What is Faceapp, how does the AI filter make you look old, and is it free to download?

SELFIE fans can now change genders, make themselves look younger or become beautiful with just one click of a button - thanks to FaceApp.

And now celebs have started the Old Age challenge where they can edit photos to show younger or older versions of themselves.

FaceApp, developed in St Petersburg, Russia, has been making waves on social media with its functions that allow users to see what they'd look like older, younger, with a different hair colour or gender.

The app can also turn blank or grumpy expressions into smiling ones. And it can tweak make-up styles.

This is done with the help of artificial intelligence (AI). An algorithm takes the input picture of your face and adjusts it based on other imagery.

This makes it possible to insert a toothy smile, for instance, while adjusting lines around the mouth, chin and cheeks for a natural look.

Is the app free to download?

You can try the old age filter at no cost for three days, but you'll need to upgrade to the pro version to unlock all of the alteration options.

The FaceApp Pro function costs an extra £3.99.

Is it safe to use?

Since the face-editing tool went viral, some have raised concerns over its terms and conditions.

They argue the company takes a cavalier approach to users' data - but FaceApp said in a statement most images were deleted from its servers within 48 hours of being uploaded.

The company also said it only ever uploaded photos that users selected for editing and not additional images.

What about facial recognition?

Others have speculated that FaceApp may use data gathered from user photos to train facial recognition algorithms.

This can be done even after the photos themselves are deleted because measurements of features on a person's face can be extracted and used for such purposes.

Celebs on the app

Celebs have jumped on the bandwagon (and we've mocked up a few on our own)...

Lauren Goodger

Susanna Reid

Victoria Beckham

Holly Willoughby

Meghan Markle

David Beckham

Harry Styles

Kate Middleton

Curtis Pritchard

Maura Higgins

Anton Danyluk

Tommy Fury

Molly-Mae

Anna Vakili

Sam Smith

Mark Wright

Charlie Brake

Mark Zuckerberg

Ron Weasley

Jordan Banjo

Conor Maynard

Dan Osborne

Ricci Guarnaccio

Ludacris and Tyrese Gibson

Tommy Mallett

Jack Fincham