Dark chocolate sold in the U.S. is often a little more like milk chocolate than manufacturers might want to admit.

An investigation by the Food and Drug Administration (FDA) conducted earlier this year found that a lot of dark chocolate contains milk—even when it says it doesn't. A new consumer update elaborates on the findings, as well as the risks posed by what the agency has identified as a worrisome area for consumer misinformation.

"Unfortunately, you can't always tell if dark chocolate contains milk by reading the ingredients list," the report warns.

Of the 94 total samples the FDA tested, only 6 listed milk as an ingredient. Over 60 percent of them, however, contained milk. Seventy-five percent of those that warned the chocolate "may contain milk," did indeed have dairy. Thirty three percent of those that didn't mention milk at all on the label, still contained it. And 15 percent of dark chocolate samples that said they were "dairy-free" or "lactose-free," actually weren't.

Manufacturers, to be clear, aren't purposely injecting their 75 percent cacao bars with dairy, according to the FDA. Rather, the reason why dark chocolate manufacturers seem to be having so much trouble keeping traces of milk out of their product is likely that the same equipment that is used to make dark chocolate is often also used to make milk chocolate, which is roughly 10 to 12 percent milk.

Still, the prevalence of milk in products that clearly promise to come milk-free is troubling. Dairy, after all, is one of eight major food allergens. All food products that contain milk must say so, according to U.S. law.

While chocolate can contain traces of milk and yet still be considered dark, the frequency with which samples were found to have dairy despite no intimation poses a risk to those with milk allergies, and may undermine the integrity of industry oversight. What's more, the findings raise questions about whether those hoping to avoid animal products entirely can count on commercially sold dark chocolate.

At the moment, the FDA recommends that consumers hoping to avoid milk be wary of dark chocolate products, including those that clearly state they are dairy-free.