Major food allergens are those that can cause severe and even life-threatening reactions. Previously, the eight major food allergens included milk, egg, soy, wheat, peanut, tree nuts (e.g., walnuts, cashews), crustacean shellfish (e.g., shrimp, lobster), and fin fish (e.g., bass, cod). Together, these eight allergens account for over 90% of the serious allergic reactions to foods in the United States.

The Food Allergen Labeling and Consumer Protection Act (FALCPA) of 2004 recognized the eight major food allergens and described how they must be identified. This is done in two ways - first, any ingredient that is a member of these eight groups must be identified with the name of the major allergen group in parentheses (e.g., "whey (milk)" or "lecithin (soy)"). Second, following the ingredient list must be a "Contains" statement that simply and clearly lists the major food allergens present (e.g., "Contains: milk, soy"). This makes it easier for people with severe food allergies to identify the foods that contain allergens that might cause a severe reaction. Not required, but often voluntarily included, are statements that the food is "Made in a facility that processes..." or "May contain traces of..." to indicate that cross-contamination of major food allergens not specifically included in the food product may have occurred during manufacturing, to warn people who are extremely allergic that they might react to the food.

The Food Allergy Safety, Treatment, Education, and Research Act of 2021 added sesame as the ninth major food allergen in the US. This is because of the number of people who have severe reactions to sesame, and recognizes that as few as 20-30% of these people outgrow their sesame allergy. Labeling for sesame allergen content took effect as of January 1, 2023 but did not apply to food already produced, packaged, and on the shelves. So be aware that for a few weeks, there will be foods in stores that contain sesame allergen but might not have the newly required labeling.

An important note of caution, however. There have been reports of companies adding sesame to products that previously did not contain sesame. Some companies claim that some products that do not contain sesame are made in facilities in which cross contamination with sesame might occur, and feel that it will be too expensive to change their processes to guarantee that products are free of sesame. Thus, to make sure that people do not react to small amounts of sesame contamination, they add sesame so that their products have to be clearly labeled as containing sesame. However, this means that people with mild sesame allergy that previously tolerated cross contamination in their favorite foods might now suffer severe reactions to particular brands of foods that were previously known to be safe, because the manufacturer is now deliberately adding sesame.

If you have a severe allergy to any of these major food allergens, please remain vigilant in reading labels of the foods you eat!