What is the one thing that young people fear more than anything? Head lice. The social nightmare of being diagnosed with having tiny creatures eating up your scalp is second to none.

What is the one thing that young people love more than anything? Selfies. The trend became so big over the last few years that it was named the word of the year by Oxford English Dictionary in 2013.

But could there be a connection between the two? Could selfies be spreading head lice? A San Francisco expert has reason to believe they do.

Marcy McQuillan of Nitless Noggins, a lice treatment clinic, told SFist that more and more teens and early adults are coming in with cases of lice. She says it’s because young people taking selfies will squeeze friends into the shot, bringing their heads into close contact with each other.

That gives lice a chance to jump from person to person.

Lice is usually more common in younger children, who come into head-to-head contact out on school playgrounds and by sharing headwear.

“Every teen I’ve treated, I ask about selfies, and they admit that they are taking them every day,” says McQuillan, “I think parents need to be aware, and teenagers need to be aware too.”

So all you young folk out there, be careful whom you take selfies with, because an Instagram selfie from inside a lice treatment center won’t be good publicity. Or you could do everyone a favor and not take selfies at all.

Medicine