In at least two cases, sexting has been linked to suicide but a new poll shows more than a quarter of young people in the US are "sexting" - sharing nude photos, videos and chat by mobile phone or online, with the fad only becoming more common as people get older.

13-year-old Hope Witsell hanged herself after relentless taunting at her school near Tampa, Florida.

She had sent a nude photo of herself to a boy she liked, and another girl used his phone to send the picture to other students who forwarded it along.

The St. Petersburg Times first reported on Hope's death this week.

And last year in Cincinnati, 18-year-old Jessica Logan hanged herself after weeks of ridicule at school.

Logan had sent a nude cell phone picture to her boyfriend and after they broke up, he forwarded the picture to other girls.

While one-quarter of teenagers have 'sexted', around one-third of young adults taking part in the poll said they had been involved in sexting.

Thelma, a 25-year-old from Natchitoches, Louisiana, who didn't want her last name used, said she's been asked more than once to send naked pictures of herself to a man.

"It's just when you're talking to a guy who's interested in you, and you might have a sexual relationship, so they just want to see you naked," she said, adding that she never complied with those requests.

"But with my current boyfriend, I did it on my own; he didn't ask me," she said, adding that she was confident he would keep the image to himself.

Those who sent nude pictures of themselves mostly said they went to a boyfriend, girlfriend or romantic interest.

14 per cent said they suspect the pictures were shared without permission, and they may be right.

Seventeen per cent of those who received naked pictures said they passed them along to someone else, often to more than just one person.

Boys were a little more likely than girls to say they received naked pictures or video of someone that had been passed around without the person's consent.

Common reasons were that they thought other people would want to see, that they were showing off and that they were bored.

Girls were a little more likely to send pictures of themselves, while boys were more likely to say that sexting is "hot" and most girls called it "slutty."

Altogether, 1 in 10 pollsters said they had sent naked pictures of themselves on their cell phone or online.

Around 50 per cent said sexting was a serious problem — and did it anyway.

"There's definitely the invincibility factor that young people feel," said Kathleen Bogle, a sociology professor at La Salle University in Philadelphia and author of the book "Hooking Up: Sex, Dating, and Relationships on Campus."

"That's part of the reason why they have a high rate of car accidents and things like that, is they think, 'Oh, well, that will never happen to me,'" Bogle said.

Research shows teenage brains are not quite mature enough to make good decisions consistently.

By the mid-teens, the brain's reward centres, the parts involved in emotional arousal, are well-developed, making teens more vulnerable to peer pressure.

But it is not till the early 20s that the brain's frontal cortex, where reasoning connects with emotion, enabling people to weigh consequences, has finished forming.

Beyond feeling invincible, young people also have a much different view of sexual photos that might be posted online, Bogle said.

They don't think about the idea that those photos might wind up in the hands of potential employers or college admissions officers, she said.

"Sometimes they think of it as a joke; they have a laugh about it," Bogle said.

"In some cases, it's seen as flirtation. They're thinking of it as something far less serious and aren't thinking of it as consequences down the road or who can get hold of this information. They're also not thinking about worst-case scenarios that parents might worry about."

Already, young people in Florida, Indiana, Ohio and Pennsylvania have faced criminal charges, in some cases felony charges, for sending nude pictures but charges aren't the worst consequences.

The poll is part of an MTV campaign, "A Thin Line," aiming to stop the spread of digital abuse.

The AP-MTV poll involved 1,247 people aged 14-24 and has a margin of sampling error of plus or minus 2.8 percentage points.

The survey was conducted by Knowledge Networks, which initially contacted people using traditional telephone and mail polling methods and followed with online interviews.

People chosen for the study who had no Internet access were given it for free.