The allure of the blockbuster "Twilight" books and movies appears to have spawned a troubling trend: Teen couples are biting one another to show affection, sometimes biting so hard they draw blood.
"Biting is challenging because one of the things we know about sexuality and biting and vampires is that it's passion, it's all-encompassing, it's wanting to consume someone else," New York City sexologist Logan Levkoff told "Good Morning America."
"And biting is sort of an extension of the hickey. It's that same thing about marking someone else and showing passion."
Michael Kaplor, 16, said he has been biting his girlfriend on and off for about a year.
"For me, biting is the way to show affection toward the other person and to just get a crazy adrenaline rush and not so much to mark territory or to show I belong to something, but just to show the other person I care and there's a deeper sense of affection," he said.
He bites his girlfriend on or around her shoulder to ensure the marks remain hidden. The teen said he draws no blood but knows of others who do.
"I think a lot of people draw blood because they want to feel very powerful, when you bite the other person you get the huge adrenaline rush and it feels like you can't stop and some people just take it too far," he added.
The urge to push the envelope can come with serious consequences.
Up to 15 percent of bites from humans can become infected and, in rare cases, biting can spread blood-borne diseases including hepatitis, syphilis and HIV, doctors say.
Even so, teens are drawn to the practice, Levkoff said.
"It gets to that whole obsessive, compulsive, overwhelming teen sexuality, which is, 'We have all these new feelings, we don't know how to control them, we don't know how to make sense of them.' And for some reason, because it's on the screen, because it seems powerful and sexual, we want to mimic it. It doesn't make it right," she added.
But some teens aren't interesting in receiving -- or giving -- this very literal love bite.
Paola Hernandez, 15, said a boyfriend tried to pressure her to allow herself to be bitten.
"He said, 'I love you' and that's the way I want to show you," she said. "I didn't give in because it was kind of idiotic."
She said some of her classmates, mimicking on-screen vampires, even cut their skin so they can taste one another's blood.
"That means you're stuck with them, they have your blood inside of them and you have their blood and so you're closer to each other," she said.
Some teens are even posting their adventures in biting on the Internet. Videos have popped up on YouTube and there are even Facebook pages devoted to the subject.
Missy Wall, program director for Teen Contact, a Dallas organization that provides a hotline for teens who are in trouble and classes for teens and their parents, said biting is becoming a modern-day love tap.
"There are even teenagers that have tattoos of bite marks, so I think it's not just they're trying to mimic the hickey," she said. "I think they're trying to mimic what they're seeing in the media and on TV and they're wanting to experience it."
Vampires have become a huge part of pop culture.
The "Twilight" movies, "Twilight," "New Moon" and "Eclipse," have broken box office records, while "True Blood" -- the HBO hit that also is based on a bestselling series of books -- was nominated for several Emmy Awards Thursday.