Too many young people in the UK remain unaware of the risks of HIV and other sexually transmitted infections, a healthcare charity has said.
The young need to be better informed about sex, the NAT says
A National Aids Trust survey found 25% of 15-24 year-olds stop using condoms if they or a partner go on the Pill.
At the start of National Condom Week, the NAT has called for "urgent improvements" in sex education.
It backs the campaign to make sex and relationships education compulsory on the national curriculum in England.
The trust said its survey's findings suggested many young people "do not see condom use as a way of protecting their sexual health".
The Ipsos MORI survey of 2,048 people aged 15 and over, commissioned by the trust, found public awareness among all age groups of how HIV is transmitted has seriously declined over the last five years.
Some 53% of all women surveyed said they would always use a condom with a new sexual partner, compared to 39% of men.
When it came to young people aged 15 to 24, 55% said they would always use a condom with a new sexual partner, compared with 22% who would "usually" and 12% "sometimes" use a condom.
Apart from the over 55s, those aged 15-24 were found to be least aware of the protection condoms offer against STIs.
They also had the lowest knowledge of the risks of HIV transmission through sharing syringes.
NAT chief executive Deborah Jack said: "Too many young people fail to realise that using a condom with a new sexual partner is a vital protection not only against pregnancy but also against HIV and other sexually transmitted infections.
"The government must act now to ensure consistent education around condoms and sexual health in schools, ending the current postcode lottery."
Lisa Power, Head of Policy at Terrence Higgins Trust, said sex education in schools needs to "move beyond just the biological aspects".
"Traditional teenage pregnancy work also tends to focus on the pill and long acting contraceptives, rather than promoting condoms and highlighting the risks of STIs," she said.
"Young people need all the information about sex, not just some of it."