The soaring rate of sexually transmitted infections was last week laid at the door of young people – and particularly women in the rather broad age grouping of 15 to 24, which encompasses adolescent schoolgirls, careerists and young mums. There was talk of the "vulnerability" of some young women, unable to talk to their boyfriend about using a condom – or maybe even whether to have sex at all. And there were the usual knowing assumptions about the sex drive and carelessness of youth.

But there are a few other things underlying the bald data put out by the Health Protection Agency revealing nearly half a million (482,696) STI diagnoses in the last year. One of those is the slightly dull fact that testing has become much more sensitive, picking up infections that might have been missed in the past. Another is that more people are being tested – and much of this has to do with the national chlamydia screening campaign. It is aimed at the under-25s, and while it targets both men and women for testing, it is more likely to attract women because chlamydia has a more alarming effect on them. The asymptomatic STI, left without treatment, can make them infertile.

Chlamydia diagnoses were by far the biggest group of STIs reported by the HPA. There were 217,570 diagnoses in 2009 – a rise of 7% since last year – more than for any other sex infection. The numbers are very much smaller for gonorrhoea – 17,385 last year – syphilis (3,273) and genital herpes (30, 126). Chlamydia diagnoses were more than double even the second largest group, genital warts, which showed a decrease to 91,257.

The chlamydia screening campaign was criticised last year by the National Audit Office for wasting money – including offering opportunistic tests at music festivals and in nightclubs – and lambasted by Edward Leigh, chairman of the House of Commons public accounts committee, who said it had been unthinkingly rolled out.

But the committee was not suggesting scrapping it. In a report in January, it said screening was crucial to improving young people's sexual health and accused the government of a lack of urgency over the issue. Instead of relying on local primary care trusts to roll out their own programmes, there should be national implementation, the committee said.

Screening has only reached a small percentage of the eligible age group, but it did treat 38,000 young people for chlamydia in 2008/9. And there is another important, positive effect. Getting tested for chlamydia – or even considering having a test – inevitably makes young people think and possibly talk about their sexual health.

That's the hard bit for the public health experts. Awareness campaigns are difficult. Radio commercials, featuring young people talking about carrying condoms in their bags when they go clubbing, are not always going to overcome the hang-ups of most young men and women when it comes to raising the issue at the crucial moment. Sex is a matter of emotion and excitement, not calculation and judgment.

The most successful awareness campaign on sexual behaviour was the one that featured the iceberg ads on TV, warning that HIV/Aids was something that could kill us all. No anti-STI campaign is going to hit that hard these days, when even HIV can be held at bay by drug treatment. And HIV rates are steadily rising now too.

So this is why the almost universal cry last week was for better sex education in schools. They are talking about more than a chat about what goes where. What is needed is not so much sex education as sexual relationships education – a far trickier thing to teach. It's not about how you put on a condom so much as how we negotiate each other. It's about respect for oneself as well as one's partner and it needs to start young. The peak age for sexual infections in women is 19 to 20 and for men, 21 to 23. That's far too late to be learning these particular lessons.