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Last Updated: Thursday, 31 March, 2005, 00:03 GMT 01:03 UK
Late developers' sex risk warning
Chlamydia cells
Chlamydia can cause infertility
Late developers may be more vulnerable to high risk sexually transmitted diseases, research suggests.

The risk of being infected seems to be more closely linked to the age a person reaches sexual maturity than starting to have sex when young.

The researchers, from the University of Manchester, believe that girls who mature early may be protected to some extent by their hormones.

Details are published in the journal Sexually Transmitted Infections.

It is important that young women entering a new relationship do emphasise the use of contraception
Dr Simon Barton,
British Association for Sexual Health and HIV

The researchers studied 127 young women from three sexual health clinics.

All of them had started having periods within the preceding five years or were aged 17 years and under.

The women were screened for genital infections, including chlamydia, human papillomavirus (HPV) and bacterial vaginosis.

Almost two thirds of the young women tested positive for HPV - half of which were the high risk types associated with the development of cervical cancer.

Over half of those infected with HPV had at least one other infection.

About one in four tested positive for chlamydia, which is associated with infertility.

Oestrogen aid

The researchers found that specific behaviour patterns had specific effects on particular infections.

A recent new partner or use of a condom was associated with a lower risk of chlamydial infection, while the use of emergency contraception doubled the risk.

Sex during a period also increased the risk of bacterial vaginosis, while smoking conferred protection against HPV.

But sexual maturity had a significant impact on all three infections.

More sexually mature women were significantly less likely to have any of the infections.

The association held good even after other factors, such as number of sexual partners were taken into account.

The researchers believe the key may be that girls who reach sexual maturity early have high levels of the female sex hormone oestrogen.

Researcher Dr Loretta Brabin said this might help to reduce the risk of infection by accelerating physical development.

'Myth dispelled'

There are a number of defence mechanisms which are mobilised when a woman becomes sexually mature.

The production of cervical mucus can help block infections from penetrating the cells of the vagina and cervix, while the environment in the vagina becomes more acidic and thus less hospitable to infections.

In addition, cells from the cervix, called columnar cells, which protrude down into the vagina before sexual maturity and which are particularly vulnerable to infections such as chlamydia, mature and lose their vulnerability.

Dr Brabin told the BBC News website: "Our findings dispel the myth that vulnerability to sexual infection is all about the age of onset of sexual activity and high risk behaviour."

But she stressed no young woman should indulge in risky sexual behaviour - particularly as this research suggested they were more likely to contract multiple sexual infections.

Dr Simon Barton, of the British Association for Sexual Health and HIV, said the risk of contracting a sexually transmitted infection were influenced by a number of factors, including a person's genetic make up and whether they already had other infections.

He added it was "important that young women entering a new relationship do emphasise the use of contraception".


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