Most food allergies start in childhood, but they can develop at any time in a person's life. It isn't clear why, but some adults develop an allergy to a food they could once eat with no problem. Sometimes, a child outgrows a food allergy only to have it reappear in adulthood.
If you have a food allergy, you'll need to avoid the offending food altogether. An allergic reaction can quickly put your immune system into a state of emergency, affecting numerous organs in your body. For certain people, even a tiny amount of the food may cause symptoms such as digestive problems, hives, facial swelling or trouble breathing. Some people with a food allergy are at risk for a life-threatening reaction (anaphylaxis) that requires emergency treatment.
However, most food reactions aren't caused by a true food allergy. They're caused by a food intolerance, which is generally limited to digestive problems. With an intolerance, you may be able to eat small amounts of the offending food without a reaction.
Don't ignore a reaction that occurs shortly after eating a particular food. See your doctor to determine what's causing it. Even if you've had a relatively mild reaction in the past, subsequent allergic reactions may be more serious. Get emergency treatment for any severe food reaction.