Right at this very moment, thousands of teenagers are taking a selfie with their phones or tablets. The trend has exploded over recent years, enough to get selfie in the Merriam-Webster dictionary, but experts are sending out a warning - don't let this habit get out of hand.

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People have been taking pictures of themselves for ages, but these days, it can be done much quicker and cheaper, and the world can see your close-up in an instant.

Deborah Carr, a sociology professor at Rutgers University, said selfies are a way for our kids to "put their best face forward" and seek approval. That approval comes in the form of likes and comments on Facebook, Instagram and other social networks.

Carr said teens shouldn't be discouraged from taking pictures of themselves and creating an identity online, but kids and their parents alike should follow some common sense ground rules.

"Kids of any age should look age-appropriate," Carr said. "It starts to be dangerous if a 14-year-old girl takes a selfie of herself and she looks 18 or 19. If that falls into the wrong hands or attracts the wrong attention, that could be problematic."

It would also be wise to avoid any inappropriate behavior or paraphernalia in these photos. Carr said unsavory details can haunt a teenager later on in life.

"We know that employers look at peoples' Facebook pages when they're thinking of hiring them for a job, even a fast food job," she explained.

Some people, meanwhile, don't understand when enough is enough. As someone's selfie count rises, perhaps to a few posts per day, that person can gradually go from cute and appealing to annoying and self-absorbed.

Carr said these personal photos have also caused plenty of issues for adults, especially in the world of online dating. Anyone's profile shot can be one that's heavily doctored and unrealistically attractive, but reality sets in when people meet face-to-face.