Public health advocates often use the phrase natural in their attempts to promote breast-feeding. As a marketing strategy, it’s a shrewd move. Most mothers will feel at least a little bit guilty about going the “unnatural” route and will be too tired to question the speciousness of what’s being implied. But as a public health strategy, this use of natural may not be a very wise move at all.

In a new paper recently published in Pediatrics, bioethicists Jessica Martucci and Anne Barnhill argue that the emphasis on the “natural” aspects of breast-feeding can easily backfire. By endorsing breast-feeding as natural, they say, breast-feeding advocates are reinforcing the idea that natural is A) something that actually exists and B) healthier. By setting up this dichotomy, these pro–breast-feeding campaigns might serve as unintentional fodder for concerns against “unnatural” interventions like vaccinations.

“The idea of the ‘natural’ evokes a sense of purity, goodness, and harmlessness,” Martucci and Barnhill write. “Meanwhile, synthetic substances, products, and technologies mass produced by industry (notably, vaccines) are seen as ‘unnatural’ and often arouse suspicion and distrust. Part of this value system is the perception that what’s natural is safer, healthier, and less risky.”

There are currently no studies demonstrating a direct link between the promotion of breast-feeding as natural and the rise of parents who don’t vaccinate their children. Still, it’s not hard to find examples of how this unwavering, and often unfounded, preference for all things natural feeds such beliefs. One popular parenting writer whose blog is titled “Mama Natural,” says that instead of vaccines she finds “natural and gentle ways to boost [her son’s] immunity.” Or as a mom explains in the documentary film The Vaccine War: “As a parent, I would rather see my child get a natural illness and contract that the way that illnesses have been contracted for at least 200,000 years that homo sapiens have been around.”

Martucci and Barnhill also point out that to describe breast-feeding as natural is to make a number of assumptions about gender roles and family life. Are two gay dads raising their child unnaturally if they formula-feed? What about a family who adopts? Or a mom who can’t or doesn’t want to breast-feed? Surely, these are all environments in which a baby could thrive.

In a recent paper from the Nuffield Council on Bioethics, an independent ethics organization based in the U.K., the authors consider how mushy a category “natural” is and whether it’s time to get rid of it.

“The concept of nature itself, and perceptions about the link between nature and value, also change and are reflected differently in philosophy, social science, and literature at different points in history,” they write. “Associating what is natural with what is good and what is unnatural with what is bad is not, therefore, straightforward: It is difficult to define natural and unnatural things or processes.”

They conclude the paper by recommending that scientists, governments, and doctors stop using the phrase natural—which, they determine, has no fixed meaning—unless they are very clear about the beliefs and values behind it. I’d love to see the rest of us do the same.