Q: The other day I bought a clear plastic ruler, and when I arrived home I discovered that it had a tiny label that read: “WARNING: This product contains chemicals known to the State of California to cause cancer and birth defects or other reproductive harm.” What does this label mean, and should I avoid products that have it? —Laura Guy, Ridley Park, PA

A: The warning label you refer to is an artifact of a California ballot question—the Safe Drinking Water and Toxic Enforcement Act of 1986 (better known as Proposition 65)—designed to alert consumers to the presence of toxic substances in products they might purchase.

Proposition 65 and the campaign from which it emerged were part of a national, statewide, and local right-to-know effort starting in the mid-1980s. The movement emerged largely in response to the incidents in Bhopal, India—in 1984, methyl isocyanate gas escaped from a chemical facility and killed thousands of people in the first night alone, with thousands more dying in the weeks, months, and years that followed. The disaster, and the chaos that ensued, prompted many to call for access to information about the plants in their own vicinities. In the United States at the federal level the result was the Emergency Planning and Community Right-to-Know Act of 1986. While the provisions in the national legislation focused on community preparedness in case of disaster (like that in Bhopal), the right-to-know movement began to argue for access to information related to chemicals in everyday life. State-based initiatives, like Proposition 65 in California, were predicated on the idea that toxic exposure could result from handling products casually, not just during emergencies, and therefore the public had a right to know what chemicals they were coming in contact with in their daily lives. The right-to-know movement provides a crucial platform for supplying information to citizens so that they, as individuals, can make decisions about the products they choose to use—which leads me to your question.

The short answer to your question is that it’s up to you. By providing information to the individual, laws like Proposition 65 attempt to create a situation where access to information means better decisions. But the case is not clear-cut.

Should you decide not to heed this warning, you have to realize that you are using a product that (at least in the state of California) is recognized as toxic. Maybe that’s okay. You probably won’t be eating the ruler. But you are coming into contact with it. And since you don’t know what chemical (or chemicals) prompted the warning, what specific threats or hazards they pose, or exactly what the routes of exposure for those chemicals happen to be, you might decide that it is no big deal.

Should you decide not to heed this warning, you have to realize that you are using a product that (at least in the state of California) is recognized as toxic.

If you decide that you’d like to avoid these products, you’ll now find yourself dealing with an entirely different dilemma. The plastic ruler you purchased contains a chemical registered in the state of California as toxic. Odds are, however, that the other rulers sitting alongside that one also have known toxins—most likely the same ones. You might choose a wooden ruler instead, I suppose, but perhaps that won’t suit your needs. The problem now is finding the product you need but without the label. You still don’t know what exactly it is you’re trying to avoid, chemically, so instead you’re stuck trying to avoid the label, which is likely present on more products than you realize.

Your question, and my difficulty answering it, point to an ongoing problem with right-to-know initiatives. What information do you have a right to know? How much do you have a right to know? And what can you reasonably be expected to do once equipped with this information? In the case of the federal right-to-know legislation the intention appears to be fairly clear: you need to know enough to understand that there may be an imminent hazard nearby. But with the state-based right-to-know cases, such as that in California, the situation created by labels and warnings often introduces confusion rather than empowerment. Now that you know you might be harmed by unnamed chemicals in your consumer product, you are faced with an unanswered question: how do I protect myself? Even worse, the proliferation of the labels without any clear direction likely means that for all intents and purposes the labels themselves disappear. I don’t mean to downplay the need for right-to-know efforts. In fact, your question prompts us to see that we actually need to know more. And that problem can’t be solved with a label.