New research published this month suggests that food shoppers may be most confused by labels that say products “may contain” allergens.

Allergens included as intended ingredients must by law be identified on the label. Precautionary labeling, however, is voluntary. Precautionary labels identify foods that have shared equipment with allergen-containing foods. Though the allergens aren’t included intentionally, trace amounts from shared equipment may still be enough to trigger a reaction.

Confusion arises, the study says, between foods identified as containing allergens and those that simply “may contain.” Many consumers reported buying foods that simply listed they “may contain” allergens, despite being allergic to those foods.

Research leaders FARE and Food Allergy Canada suggest a single, mandatory “may contain” label for all allergen- and potentially allergen-containing foods. Another solution, researchers say, might be to require labels to list specific amounts of allergens in their products.