Bisphenol A, commonly known as BPA, may be among the world’s most vilified chemicals. The compound, used in manufacturing polycarbonate plastic and epoxy resins, is found in plastic goggles, face shields, and helmets; baby bottles; protective coatings inside metal food containers; and composites and sealants used in dentistry. As animal studies began to show links between the chemical and breast and prostate cancer, early-onset puberty, and polycystic ovary syndrome, consumer groups pressured manufacturers of reusable plastic containers, like Nalgene, to remove BPA from their products. Warnings went out to avoid microwaving plasticware or putting it in the dishwasher. On May 6th, the President’s Cancer Panel issued a report deploring the rising number of carcinogens released into the environment – including BPA – and calling for much more stringent regulation and wider awareness of their dangers. The panel advised President Obama “to use the power of your office to remove the carcinogens and other toxins from our food, water, and air that needlessly increase health care costs, cripple our Nation’s productivity, and devastate American lives.” Dr. LaSalle Leffall, Jr., the chairman of the panel, said in a statement, “The increasing number of known or suspected environmental carcinogens compels us to action, even though we may currently lack irrefutable proof of harm.”

The narrative seems to follow a familiar path. In the nineteen-sixties, several animal studies suggested that cyclamates, a class of artificial sweetener, caused chromosomal abnormalities and cancer. Some three-quarters of Americans were estimated to consume the sweeteners. In 1969, cyclamates were banned. Later research found that there was little evidence that these substances caused cancer in humans. In the nineteen-eighties, studies suggesting a cancer risk from Alar, a chemical used to regulate the color and ripening of apples, caused a minor panic among parents and a media uproar. In that case, the cancer risk was shown to have been overstated, but still present, and the substance remains classified a “probable human carcinogen.” Lead, too, was for years thought to be safe in small doses, until further study demonstrated that, particularly for children, even slight exposure could result in intellectual delays, hearing loss, and hyperactivity.

There is an inherent uncertainty in determining which substances are safe and which are not, and when their risks outweigh their benefits. Toxicity studies are difficult, because BPA and other, similar chemicals can have multiple effects on the body. Moreover, we are exposed to scores of them in a lifetime, and their effects in combination or in sequence might be very different from what they would be in isolation. In traditional toxicology, a single chemical is tested in one cell or animal to assess its harmful effects. In studying environmental hazards, one needs to test mixtures of many chemicals, across ranges of doses, at different points in time, and at different ages, from conception to childhood to old age. Given so many variables, it is difficult to determine how harmful these chemicals might be, or if they are harmful at all, or what anyone can do to avoid their effects. In the case of BPA and other chemicals of its sort, though, their increasing prevalence and a number of human studies that associate them with developmental issues have become too worrisome to ignore. The challenge now is to decide a course of action before there is any certainty about what is truly dangerous and what is not.