Some teenagers are failing to use condoms properly, risking unwanted pregnancies and sexually transmitted infections, a snapshot study suggests.
Teenage couples would benefit from better safe sex advice, experts say
Southampton University researchers surveyed just under 1,400 teenagers aged 16 to 18 across England.
Around half had had sex. Of the 373 who had used a condom on the most recent occasion, 6% had put one on too late and 6% had removed one too early.
Experts said the Sexually Transmitted Infection journal study was worrying.
The researchers also asked just over 100 teenagers to keep a diary of their sexual activity for six months.
Of the 74 who said they had used a condom, 31% had put it on after penetration had already occurred, and 10% had taken a condom off too early on at least one occasion during that time.
Of the 714 diary entries given to the researchers, a condom was not used during sex on 322 occasions.
'Skills and knowledge' key
The most common reasons for not using a condom were to enhance intimacy, because sex felt better without one, because other contraception was being used, or because couples got "carried away".
Those who had chosen to use a condom did so to avoid pregnancy, to avoid "making a mess", and to make sex last longer.
The researchers found few said the prevention of sexually transmitted infections was a reason.
The researchers did find that boys who were able to talk openly to their mothers during their early teenage years were more likely to use condoms correctly.
The study was led by Professor Roger Ingham, of the Centre for Public Health Research, at the University of Southampton.
Writing in Sexually Transmitted Infections, the researchers said: "If we are to see a reduction in sexually transmitted infection prevalence, it is essential that young people understand the importance of using condoms consistently and correctly, and are also equipped with the skills and knowledge to do so."
Toni Belfield, of the Family Planning Association (FPA), said: "This research continues to reinforce the message that young people need good information and support to use condoms correctly and consistently.
"Good communication with a trusted adult is an essential part of this support.
"We would urge parents and carers to be open about sex and relationships with their children, so they can be a source of guidance for them."