Women have been warned against the use of feminine hygiene products, after scientists found that incorrect usage can affect hormone levels.
When used internally, for "vaginal douching", these products can impact oestrogen, testosterone and thyroid hormone levels, researchers warn.
Women are being urged to use the products to wash externally (the vulva and labia) rather than internally (the vagina), as internal use can expose users to harmful chemicals known as "phthalates".
The study took urine tests from 739 women to detect phthalate exposure. The female participants were also questioned about their douching habits and use of other feminine care products.
Researchers found that the more a woman "douched", the higher her exposure to a form of diethyl phthalate (DEP).
In women who douched at least once a month, there were 52% higher concentrations of a form of phthalate found in their urine, and those who douched at least twice a month had 152% higher DEP concentrations in their urine than non-douchers.
Researchers also found no link between DEP and other feminine hygiene products such as tampons, sanitary towels, powders and sprays.
"Douching is not medically required," said lead author, Ami Zota from George Washington University. "A healthy vagina has an effective self-cleaning system."
Zota added that doctors generally advise against douching as it can increase a woman's risk of bacterial vaginosis, pelvic inflammatory disease, pregnancy complications and potentially cervical cancer.
For those who want to keep downstairs clean and fresh, sex and relationships expert Tracey Cox recommends using an external, soap-free feminine wash.
"A healthy vagina is 'self-cleaning' and has a pleasant odour, so there's no need to douche," she tells HuffPost UK Lifestyle.
"If you do feel the need to, there could be a problem, so see your GP for a check up rather than try to mask any important symptoms - like a smelly discharge.
"I'd strongly advise using an external soap-free feminine wash," she adds, "it seems to help stop recurrences of things like thrush or cystitis. But I'd strongly advise against vaginal douching under all circumstances."
Natika Halil, chief executive of sexual health charity, FPA, echoes Cox's thoughts.
"It’s not necessary for women to use a douche," she says, "the vagina is very good at keeping itself clean and flushing water into the vagina can upset the balance of the normal bacteria.
"Douching has been linked to bacterial vaginosis, which is the most common cause of unusual vaginal discharge."
She adds: "We’ve also heard of women using douches to prevent pregnancy after sex, or to prevent sexually transmitted infections – it is ineffective in both cases."
[H/T Huffington Post]