According to a new study in JAMA Network Open, only 10 percent of Americans have food allergies, but almost double the number believe they do. 

Many of the other half may be suffering from histamine intolerance, caused by a DAO enzyme deficiency. The symptoms seen in allergic reactions, such as a runny or stuffy nose, sneezing, watery eyes, itching, headaches, hives and digestion issues, are also seen in histamine intolerance.