Teenage girls are coming under increasing pressure to text and email sexually explicit pictures of themselves, a report suggests.
The report, commissioned by the NSPCC, suggests the demands come from peers rather than from adults or strangers.
So-called sexting, the sending or receiving of sexual images by text or email, is thought to affect more than a third of under-18s.
More needs to be done to address the issue, the report concludes.
Entitled A Qualitative Study of Children and Young People , the study was conducted by researchers at King's College, London; the Institute of Education; and the London School of Economics.
"Up until now, e-safety campaigns have focused on preparing young people to face dangers posed by strangers online," said Professor Rosalind Gill from King's College, one of the authors.
"Our report suggests that the focus needs to shift to include the much more complicated issue of peer-to-peer communication and the difficulties and isolation young people experience in negotiating this," she added.
Jon Brown, head of the sexual abuse programme at the NSPCC, said the revelations were disturbing.
"What's most striking about this research is that many young people seem to accept all this as part of life. But it can be another layer of sexual abuse and, although most children will not be aware, it is illegal."
The in-depth interviews with 35 teenagers at two London schools found that girls as young as 11 were being asked to send "special photos" to boys who they knew.
In some cases, the girls had to write a name in black marker pen on a part of their body to show it was the "property" of a certain boy.
The teenagers also faced a "barrage" of messages from boys demanding for intercourse or oral sex.
"Even while we were interviewing them they were being bombarded with these messages," said lead researcher Jessica Ringrose, from the Institute of Education.
Such sexting is an extreme form of cyberbullying, the report concludes.
The study was launched at the House of Commons by Conservative MP Claire Perry.