After decades of conflicting evidence about the possible link between talc powder in the genital area and ovarian cancer, the largest study conducted to date has found no strong connection between the two.

While called “overall reassuring” in an editorial, researchers caution that the study was “underpowered” to identify a small increase in risk — because not many of the more than 250,000 women in the study developed ovarian cancer — and that some subgroups might show a possible link. More research is needed to confirm this possible association, they said.

The study, “Association of Powder Use in the Genital Area With Risk of Ovarian Cancer,” and its accompanying editorial were published in JAMA.

Some people use powder on their genitals to help control moisture and odors. The most commonly used products, such as talcum or baby powder, contain the mineral talc.

Talc has some similarities to asbestos, exposure to which has been shown to increase cancer risk. Concerns about a link between talc and ovarian cancer first arose in the 1970s, when a small study detected talc particles embedded in ovarian tumor tissue.

Since then, thousands of U.S. lawsuits have been filed by women claiming talc use caused their ovarian cancer. But the data so far have been inconclusive.

The new study is, according to the researchers, “the largest study of this topic to date.” It included data from 252,745 women, median 57 years old, collected from four large databases: the Nurses’ Health Study, Nurses’ Health Study II, Sister Study, and Women’s Health Initiative Observational Study.

This included data on the use of genital powder, though exactly how that data was collected varied among the four databases, which was a limitation acknowledged by the researchers.

They noted that “this was a highly educated group (most completed college) and most participants were white (84%–98% of each cohort).” This lack of diversity may limit the extent to which the results can be generalized.

Use of powder in the genital area was fairly common, with about 39% of the cohort reported having used it, and about 22% reporting frequent use (at least once per week). Also, one in 10 women reported using talc for at least 20 years.

Compared to those who had never used talc powder in the genital area, those who had were more likely to be black (6% vs. 3%), be obese (26% vs. 19%), or have had a hysterectomy (surgery to remove the uterus; 22% vs. 18%), and were less likely to have used birth control pills (57% vs. 64%).

With a median of more than 11 years of follow-up, 2,168 individuals developed ovarian cancer. The researchers found no significant differences in ovarian cancer risk between those who had used powder on their genitals and those who had not.

“In this pooled analysis of 4 large U.S. cohorts, there was no statistically significant association between self-reported use of powder in the genital area and risk of ovarian cancer,” they wrote.

Further investigation based on frequency of powder use revealed “no clear dose-response trends for duration and frequency of powder use in the genital area in relation to ovarian cancer risk.”

Although they found no overall indication that powder use increased ovarian cancer risk, the researchers noted that “the study may have been underpowered to identify a small increase in risk.”

In this instance, “power” refers to the sample size that needs to be in a study for a particular effect to be detected with statistical significance — that is, for random chance to be ruled out with reasonable certainty.

Basically, the researchers think it’s possible that powder use could cause a small increase in ovarian cancer risk which couldn’t be reliably detected in this cohort, but that might be demonstrated in future studies with even larger populations.

Importantly, the researchers found a slight, but statistically significant, increase in risk among powder users (by about 13%) when they included only women with a fully intact, unaltered female reproductive tract (those who had never had a hysterectomy or tubal ligation).

This may be relevant because, in theory, having an intact reproductive tract could allow powder to move from the genitals to the ovaries, where it might cause irritation and/or lead to cancer.

“This observation lends support to the hypothesis that powder … could irritate and inflame the reproductive tract, as [an intact tract] is required for there to be a direct physical path between the genitals and the fallopian tubes or ovaries,” the researchers wrote. But they stressed that, for now, “this finding should be considered only exploratory and hypothesis generating.”