Women who use shower gels and soaps in intimate areas are putting themselves at higher risk of developing sexually transmitted infections (STIs), experts have warned.
Researchers at the University of California, Los Angeles, say soaps and lubricants can damage sensitive tissues and raise a woman's chance of becoming infected with herpes, chlamydia and HIV.
Study leader Joelle Brown said there is "mounting evidence" that using these products internally can increase the risk of bacterial vaginosis - a condition that occurs when the bacterial balance becomes disrupted - and STIs.
Dr Brown's team recruited 141 women in Los Angeles who agreed to answer questionnaires about their product use and undergo lab tests for vaginal infections.
The researchers found that 66 per cent of the women reported using lubricants and cleansers internally.
The most commonly used products were sexual lubricants - 70 per cent of the product-using group used commercial lubricants, while 17 per cent reported using petroleum jelly and 13 per cent used oils.
Test results showed that the women who used products not intended for internal use, such as oils and Vaseline, were more likely to have yeast and bacterial infections, according to the findings published in the journal Obstetrics and Gynaecology.
For instance, 40 per cent of the women who used petroleum jelly as a lubricant had bacterial vaginosis - an infection that can be caused by a number of common bacterial species - compared to 18 per cent of women who did not insert petroleum jelly.
And 44 per cent of women who reported using oils tested positive for candida, the fungus that causes yeast infections, compared to 5 per cent of women who did not use oils.
Researchers suggested the increased risk for these common infections might result from the products upsetting internal pH and beneficial microbe communities, allowing harmful organisms to proliferate.
Normally, the area is home to a finely tuned system of good and bad bacteria, which produce acids that protect against infections and viruses.
Doctors do not recommend that women wash themselves internally because it can alter the balance of these bacteria and does not seem to offer any benefit.
The natural balance of bacteria in the vagina is an "evolutionary protection that is just washed away," with soaps and perfumes according to Dr Michael Zinaman, chair of obstetrics and gynaecology at St Elizabeth's Medical Centre in Boston.
A representative for Vaseline manufacturer Unilever told Reuters Health: "Vaseline Petroleum Jelly is for external use only, and we state this on our packaging for consumers. We do not recommend Vaseline Petroleum Jelly be used as a lubricant and have not performed any testing to support this use.
"Vaseline Petroleum Jelly should also not be used as a sexual lubricant in combination with latex barrier protection, as it can degrade the latex."
The study did not determine why petroleum jelly might promote bacterial vaginosis.
Commercial sexual lubricants, which are designed for internal use, were not associated with an increased risk of infection in the study, but they still require further evaluation, according to Dr Brown.
However, Dr Mary Marnach, a specialist in obstetrics and gynaecology at the Mayo Clinic in Rochester, Minnesota, claims that, many personal lubricants, like K-Y jelly, contain glycerin which breaks down to sugars and promotes yeast infections and possibly also bacterial vaginosis, noted.
"For this reason I recommend lubricants without glycerin such as Astroglide Free and those that are silicone based (K-Y Intrigue) over the counter," Dr Marnach said.
The fashion for scented intimate products can be linked to health issues, agrees Dr Sovra Whitcroft, a gynaecologist at the Surrey Park Clinic, Guildford.
She said: "The problem with perfumed products is that they change the natural pH or acidity of the vagina.
"The normal pH is four to five. If this is altered and made less acidic, it loses its natural protection and bacteria are allowed to thrive and multiply. The very product designed to improve body odour can, in a short space of time, do the opposite by contributing to an overgrowth of odour-producing bacteria.
"And many strong chemicals and perfumes can have a direct irritant effect on the sensitive mucosal lining as well as the relatively thin and delicate skin, causing contact dermatitis or inflammation. This can make the area more prone to harbouring bacteria, causing secondary infections.
"In the longer term, if products containing talcum powder are sprayed around the area, the tiny particles can be driven up into the female reproductive system.
"There have been many studies suggesting a link between these talcum particles and ovarian cancer and while it is difficult to know whether these results are true, it is important to steer clear from anything which can cause such potential harm.
"The truth is as long as a woman is healthy, washes thoroughly with soap and water frequently and changes her underwear every day there should be no need for cover-up deodorants. Using a chemical perfume to cover potential odours may mask an underlying infection or even cause one."
- DAILY MAIL