Simply cover the camera for a few seconds so enough light is blocked to activate the setting.

First things first, if you're completely new to Snapchat our complete guide to using Snapchat might be more useful, as it takes you through every element of the app. Now, tap on your face until you see a sort of mesh form over your face.

That's Snapchat mapping your face, and it's how the lenses look so realistic (and creepy).

Tap the circle at the bottom with the face swap icon to capture the image, and if you want to save it to your phone's photo library you'll need to tap the icon in the bottom left corner that looks like a downwards arrow.

You can also send it to your Snapchat friends as you normally would.

With that image saved in your photo library, you can share it anywhere, whether that's via email, on Facebook, on Twitter or elsewhere.

The popularity of Snapchat's original face swap lens doesn't seem to be slowing, so the developers have added an additional face swap option that means you can even join in the fun when you're on your own.

You can use the app's emoji stickers to add some oomph to your photos.

Choose one with the desired color and increase its size (by zooming with two fingers) so it takes up the whole screen and the edges begin to pixelate.

You can see whether you’ve sent a text or a chat – most devices show them in different colours.

Face Swap is the Snapchat phenomenon that is both disturbing and fascinating at the same time.

You should see two smiley faces appear on the main portion of the screen now.