Talc—the softest mineral on earth—historically had been a key ingredient in baby powder. Because baby powder is a cosmetic product, the Food and Drug Administration does not regulate it. But talc has faced recent legal challenges by long-time baby powder users, alleging that talc may have caused ovarian cancer.

For example, Deane Berg sued Johnson & Johnson for failing to warn of a potential link between talc exposure and ovarian cancer. Although the jury did not award her compensatory or punitive damages, it found Johnson & Johnson negligent. Other plaintiffs have now filed similar claims, alleging that talc manufacturers should warn of the alleged link between talc exposure and ovarian cancer, especially with regard to use of baby powder in the perineal area.

Plaintiffs here face several challenges in proving causation, particularly because of the tenuous link between talc exposure and cancer. A woman’s lifetime risk of developing ovarian cancer is very low: about 0.01 percent. Some studies show talc slightly increases a woman’s lifetime risk to 0.0133 percent, while other studies failed to find a link. While some epidemiological studies have demonstrated a correlation, especially in African-American women, correlation is not causation. The studies also face methodological challenges because only a few have accounted for both frequency and duration of baby powder use.

Lawsuits like these place companies in tough positions. Failure to warn claims involve balancing. The judge who presided over Ms. Berg’s case advised the jurors that they must consider both the likelihood and gravity of an ovarian cancer diagnosis caused by baby powder usage and the costs to Johnson & Johnson of including a new warning. But even in recent talc cases in which plaintiffs have been awarded damages for their claims, the jury is still out on the link between talc exposure and ovarian cancer.

Regardless, companies like Johnson & Johnson must now make a choice. They must decide whether to warn consumers that their product may cause cancer based on suspect science or face new lawsuits.