Is your baby’s bottle half empty or half full? Or is it leeching potentially dangerous levels of estrogen-like chemicals into his milk?

On May 28, an Arkansas woman filed a federal lawsuit against Playtex Products Inc. accusing the company of failing to disclose that its plastic baby bottles contained Bisphenol A, a chemical used in the manufacturing of clear plastic bottles and the linings of canned goods. The lawsuit, which is seeking class action status, contends that hundreds of studies show the BPA is toxic.

Wal-Mart and Babies ‘R Us have removed infant products containing BPA from their shelves and Senator Schumer intends to sponsor a bill in Congress to ban the use of BPA in food containers, children’s products, or products children might put in their mouths. The New York Times recently ran an editorial suggesting parents avoid BPA, also urging Congress to prohibit its use in baby bottles and cups in advance of a wider ban.

The panic about BPA in America follows Canada’s announcement in April that it will ban BPA in infant products, and the release of a report by the by the National Toxicology Program, part of the Department of Health and Human Services that noted “some concern for neural and behavioral effects in fetuses, infants, and children” and “some concern” about “effects in the prostate gland, mammary gland, and an earlier age for puberty in females.”

The problem is, “some concern” falls far below what scientists would actually consider a risk. In any case, newborns and infants are exposed to BPA at levels nowhere near what should merit alarm.

In response to the news, worried parents are tossing out their plastic bottles, and rushing to buy BPA-free alternatives. A Web site, MomsRising.org, sent out a panicked e-mail calling on mothers to “take a second to take a collective deep breath, and then mobilize for major action.”

Scientists have been studying BPA for the better part of a decade since a reproductive scientist of the University of Missouri-Columbia, Frederick vom Saal, first suggested it might pose a risk to human health. More than 4,000 studies and several major risk assessments later, scientists in the America, Japan, and the European Union have exonerated it.

But among worried parents, supposition has blossomed into fact. A blogger for MomsRising.org, Donna Norton, writes: “Over 130 studies suggest that BPA exposure, even at low doses, is linked to many health problems, including early puberty, breast and prostate cancer, obesity, attention and hyperactivity disorder, brain damage, altered immune system, and lower sperm counts.”

Ms. Norton confuses mice and men. Some scientists have observed these effects in the rodents used in the lab. It’s a huge leap to suggest that these effects have been observed, let alone studied, in human beings. There are a number of points of contention, some to do with dosages and methods of exposure in animal studies of BPA, but the crux of the matter is this: human beings and other primates metabolize BPA much more efficiently than do the rodents used in animal studies.

The health problems BPA supposedly causes are linked by credible evidence to other factors, such as genetic predisposition or lifestyle. Some, like early onset of puberty in girls, are hotly debated. While there is some discussion about whether breast development is occurring earlier in American girls, the average age of puberty — as defined at the onset of menstruation — remains unchanged at 12.75 years.

It is not that the facts are unavailable or that journalists and politicians are incapable of grasping them. It’s more that they are blinkered by a mistrust of the fruits of modernity and by deep pessimism about the future.

The willingness to assume the worst has a debilitating effect on public discussion. When scientists find nothing in claims about BPA, for instance, it is dismissed as the product of chemical industry manipulation rather than genuine and profound weaknesses with the entire thesis. Large, well-designed studies conducted by independently audited contract labs are suspect because they are “industry funded.” From this skewed perspective, even Harvard University’s Center for Risk Assessment is a shill for the chemical industry, as their 2004 report on BPA was commissioned by the American Plastics Council.

Most problematically, some groups including Environmental California routinely refer to “independent science” untainted by any ties to industry. The term is deceptive. Science is science. It stands or falls on its own merits. The notion of “independent science” actually trivializes objectivity and betrays contempt for the individual men and women involved in scientific research, both in terms of the way they conduct their own work and in the way they review the work of others.

The problem with the BPA scare is not just that parents have been frightened out of their wits about a basically benign chemical, or even the potentially huge cost of identifying alternatives and scrapping an entirely safe and effective manufacturing processes. The real problem with the BPA scare is the way it elevates fear above rational consideration of the evidence, and makes it into an organizing principle for all of society.

Ms. McDermott is a Brooklyn-based writer and chairwoman of the Park Slope Parents’ advisory board. The opinions expressed are her own.