Young people in Bradford are being warned about catching sexually transmitted infections while on holiday abroad this summer.

The drive is part of Sexual Health Week, which runs until Sunday and is focusing on the infections.

Derek Simmonds, manager of Bradford District Health Development Service, responsible for sexual health, said at this time of year people might get caught up in the holiday atmosphere or have too much to drink and behave differently to how they would at home.

"A lot of young people might end up having sex with people they had not previously met," he said.

"If they are having sex with people they don't know, they should use condoms - and also remember not to leave them in the sun, which can affect their effectiveness."

Nationally, levels of sexually transmitted infections (STIs) are on the increase.

Mr Simmonds said that, generally, levels in Bradford were no different from the rest of the country.

He said Bradford had a high incidence of chlamydia, the most commonly diagnosed STI.

"The problem is that, for many people, there are no symptoms. But later in life it can cause damage, including infertility in men and women," he said.

Mr Simmonds said while STIs were on the increase, unwanted teenage pregnancies had fallen, possibly because girls were going on the Pill.

Advice workers are asking young people to consider whether they are really ready to have sex. "We encourage people to be assertive and resist unwanted pressure," said Mr Simmonds.

As part of the national Sexual Health Week campaign, a new cinema advert starring Holby City and Spooks actress Lisa Faulkner is being shown on 20 screens.

Special posters and leaflets have also been produced.

STIs will be the focus of a course being run in Bradford schools this autumn, when teachers will work alongside health professionals. A new screensaver with information on where to get sexual health advice will be available for sixth forms and youth centres.

Mr Simmonds said the main message was "If in doubt, get checked out".

He said: "We are promoting positive relationships. They are there to be enjoyed but not exploited or abused. It is about young people caring about themselves and the other person."