The precautionary allergen labeling (PAL) like the "may contain" label is used in the food industry to warn allergic consumers that one allergen or allergens could be present in the final product while they are not part of the recipe. This PAL is not mandatory and the manufacturer must assess the risks of presence of these allergens in his plants and in finished products. According to this analysis and the implementation of preventive measures to avoid contamination, if allergens (not present in the recipe) are always found in the final products, the manufacturer will therefore decide to put a PAL. Unfortunately, according to a study between Canada and the United States, it seems that not all allergic consumers understand the use of this PAL. Confusion is present in relation to the way the statement is presented: "may contain" is taken more seriously than "manufactured in a factory that uses ...". Some consumers are not aware of the regulations around allergen labeling. And finally, consumers assumed that the PAL was used only from a certain amount of allergen. However the information to remember is that 40% of respondents buy products with PAL and therefore adopt a risky behavior. Our Ph.D. student Emilie Manny is working on allergen occurrences in proccessed foods with PAL.
If you are interested in using the precautionary statements you can read in open access the following publication which presents the use of allergen labeling in the world.