But sesame does differ in one distinct way from eggs, peanuts, shellfish, milk, and soy: The seeds are teeny tiny and hard to keep track of. This means they’re prone to “cross-contamination,” in food-allergy terms. If you operate a bakery that makes sesame bagels, the odds are decent that rogue seeds will end up in your other products, too. Bad news for people with severe sesame allergies. But it’s also expensive and frustrating for food manufacturers to ensure the seeds are kept away from other foods, if they’re on the FDA’s major allergens list.
Advocates have therefore been warning since December that the FASTER Act is poised to have a counter effect. Rather than minimize cross-contamination, as they argue the law requires, many big food brands have opted to add sesame to their bread products, then simply declare it as an ingredient. They are intentionally adding sesame flour to “avoid complying with the spirit and intent of the FASTER Act,” FARE tells Fast Company. That is cheaper than certifying that their facilities are 100% sesame-free.
From the linked article (from Jan 2023):