Phenylalanine, a naturally occurring amino acid, is not present in chewing gum products on its own. Instead, it comes from the digestion of one type of artificial sweetener, called aspartame, that is used in some chewing gums for flavoring.
Warning labels on chewing gum that indicate the presence of phenylalanine are there for the benefit of some people whose bodies cannot easily digest the chemical due to a disease called phenylketonuria. Several countries require indicating the presence of phenylalanine in gums that have been sweetened with aspartame. For those who do not suffer from the disease, phenylalanine is a simple chemical product that results from a natural digestive process.