Scientists have issued a warning to women about using talcum powder - they say it increases their risk of developing ovarian cancer.
According to researchers from Harvard Medical School, particles in the powder when applied to the genitals can travel to the ovaries and trigger a process of inflammation that allows cancer cells to flourish.
Other research has previously raised concerns over the use of talcum powder but this new study suggests women who use it are 40% more likely to develop ovarian cancer - a much greater risk than first thought.
The researchers studied more than 3,000 women and found using talc merely once a week raised the risk of cancer by 36% rising to 41% for those applying powder every day.
The study used data on 1,175 cases and 1,202 controls from a New England-based case-control study and 210 cases and 600 controls from the prospective Nurses' Health Study.
According to Dr. Maggie Gates, who led the study, until more research is done women should avoid using talcum powder in the genital area.
The study also revealed that the risks were greater still for those with a certain genetic profile - women carrying a gene called glutathione S-transferase M1, or GSTM1, but lacking a gene called glutathione S-transferase T1 ( GSTT1), were nearly three times as likely to develop tumours.
Around one in ten Caucasian women are thought to have this genetic profile, putting them at sharply increased risk.
Talcum powder is made from a soft mineral called hydrous magnesium silicate, which is crushed, dried and milled to produce powder which is in cosmetic products used by millions.
Some experts suggest it has chemical similarities to asbestos, which can cause a deadly form of lung cancer.
Laboratory tests show ovarian cells exposed to talcum powder divide more rapidly - a characteristic sign of cancer but until recently there was no proof that powder could travel through a woman's reproductive tract as far as the pelvis and then on to the ovaries.
Last year another group of doctors at Harvard Medical School identified tiny particles of powder in the pelvis of a 68-year-old woman with advanced ovarian cancer who had used talcum every day for 30 years.
The main risk factors for cancer of the ovaries include a family history of the disease, having already had breast cancer and starting periods at a young age.
Women who are overweight or use hormone replacement therapy are also thought to be more at risk.
The researchers say regular genital talcum use was associated with increased ovarian cancer risk in women with certain genetic variants and say more research is needed on these interactions and the underlying biological mechanisms involved.
The research is published in the journal Cancer Epidemiology, Biomarkers and Prevention.