A survey has found that only few young people learn about sex from their parents, with most of them getting information from television, Internet or their friends.
Only 1 percent gets lessons on the facts of life from their father and 5 percent from their mother.
Just 13 percent get most of their information during sex education lessons at school.
A staggering 81 percent find out about it from outside sources, and five per cent rely on internet porn for their knowledge, according to the survey, by Brook, the sexual health charity.
The survey questioned young people of secondary school age about where they had learnt the facts of life.
It said the reliance on outside sources had led to a series of myths developing among young people - including 33 per cent saying women could not get pregnant if it was the first time they had had sex and 25 per cent believing you could only catch HIV from gay men.
"Standards vary so widely that all too often young people miss out on the information they need to stay safe, healthy and happy," the Independent quoted Julien Hillier, deputy chief executive of Brook, as saying.