Inside Facebook recently wrote about up-and-coming Facebook apps that have seen the most growth this past week.

Although the PixFix app had been rising slowly and steadily throughout December, it topped the list, growing in the past few days from 20k users to 164k users — almost 650% growth! As you can see from the AppData graph below, there is a spike that occurred on January 30th that lasted through the 1st, allowing the app to gain 135k users in only two days – most likely the result of an ad campaign to drive traffic to the app.

PixFix is a branded app sponsored by Clearasil that allows Facebook users to edit blemishes in photos using the online tool, aptly named after Clearasil’s Ultra Treatment Cream, and then share those photos with friends. Facebook Photos is a perfect fit for a brand like Clearasil, as Facebook is the most popular photo sharing site in the world.

One parenthetical line at the bottom is the only advertisement in the entire app:

“If you used Clearasil in real life, you probably wouldn’t be in this situation.”

Clever.