While penis size, wondering if you are homosexual and the fear that masturbation makes you infertile are the questions most likely to keep teenage boys awake worrying at night.

So a Family Planning Association (FPA) survey on the top ten teenage questions about sex and relationships has found.

The importance of talking sex

The survey has been released to coincide with the start of Get Sexwise! week, which is intended to highlight the importance of parents talking to their children about sex and relationships from an early age.

Teenagers most want to discuss sex and relationships with their parents

According to the FPA, many teenagers' worries about sex and relationships "are as old as time, but some reflect the pressures on young people today to become sexually active sooner than they may wish".

The organisation wants parents and children to feel more comfortable talking about sex to each other.

Education for precaution

Previous research has shown that young people who receive a good sex education are more likely to delay their first sexual activity, and to take precautions when they begin.

They are also less likely to become pregnant. The UK currently has the highest rate of teenage pregnancies in Europe.

'Too little, too late'

A survey of young people aged between 11 and 16 showed that most thought the main source of sex education should be their parents, followed by teachers.

However many parents feel shy or embarrassed talking about sex with their children.

The FPA says that young people are unhappy with the limited sex education they receive because:

• It is too little, too late and too biological.
• Parents are unlikely to talk about sex and relationships to their children, especially if they are boys.
• More than one in 10 girls start their periods without being told anything about them.
• Young people who are gay or lesbian receive little support and face bullying in and out of school.