Lust at first photo: Tinder heats up the dating-app scene

Go ahead. Be superficial.

Tinder, an iPhone dating app, encourages users to make snap judgments about photographs of potential mates.

Part social network, part imitation of the website Hot-or-Not, Tinder promises "a fun way to meet people."

It's just one of many dating apps for smartphones, but it clearly has caught on — ranking among the top 25 social networking apps, according to AppData, a company that tracks app usage.

Sign in with Facebook, then flip through pictures of people nearby. Tap a green heart if someone catches your eye. Not interested? Tap a red "X" and move on.

If there's mutual attraction, Tinder notifies the users and offers to set up a private chat room. Go ahead and flirt via text.

Or, given a sudden change of heart, ignore the match and tap on "Keep Playing."

A relationship based on nothing but physical attraction usually doesn't last, she said.

"What do you think keeps your grandpa and grandma together after 40 years?" Davis said. "It's not because your grandpa had a hot six-pack 40 years ago."