PHILADELPHIA (CBS) – If you suffer from a milk allergy, you may want to do some research before eating that piece of dark chocolate.

A study done by the Food and Drug Administration tested 100 dark chocolate products and found that many of them contained milk, despite it not always being clearly listed on the label.

READ MORE: Sabrina Spellman Makes An Appearance On The CW's Riverdale; Kiernan Shipka Reveals 'Fans Will Get Some Clarity'

The FDA says milk is one of eight major food allergens, and U.S. law requires foods containing a major food allergen to provide its name on the label.

Researcher Binaifer Bedford, M.S., an Oak Ridge Institute for Science and Education (ORISE) says a manufacturer may not intend to use milk in a dark chocolate product, but if the dark chocolate product shares equipment with, for example, a milk chocolate product, traces of milk may inadvertently wind up in the dark chocolate.

The FDA says it conducted the study after hearing from consumers who had eaten dark chocolate and experienced a harmful reaction.

The FDA separated the dark chocolate into categories including statements such as “may contain milk” or “may contain traces of milk,” “dairy-free” or “allergen-free,” no mention of milk on the label and inconsistent statements.

The FDA found dark chocolates labeled “dairy free” or “allergen free” were the least likely to contain milk, but two of the 17 products were still found to contain some milk.

READ MORE: Christopher Gillie Charged With Arson In Fire That Killed Elderly Man In Buckingham Township

Fifty-five of 93 bars without any clear labeling of the presence of milk still contained milk.

Six of the 11 chocolate products labeled “traces of milk” contained milk at detectable levels high enough to potentially cause a severe reaction.

Bedford says, “First of all, milk-allergic consumers should be aware that a high proportion of the dark chocolates we tested contained milk, even when the label failed to list milk as an ingredient,”

The FDA says consumers who are allergic to milk should be aware that a high proportion of tested dark chocolates contained milk.

“And because consumers can’t be sure that a statement about milk is completely accurate, they may want to contact the manufacturer to find out how it controls for allergens such as milk during production,” says Bedford.

MORE NEWS: 13 Philadelphia Police Officers On Administrative Duty Over Gun Arrest Discrepancies

To read the full study, click here.