In the past few decades, food allergies have exploded. As their numbers rise, more people are conscious of what they eat and how it's prepared. In grocery stores and on restaurant menus, you'll find offerings that are peanut-, gluten-, or dairy-free, all catering to these growing markets. But while people may abstain from a particular substance, the reasons for their avoidance may be quite different. What does it mean to be allergic to something, as opposed to intolerant or sensitive?

Food Allergy

A true food allergy means the body mistakes the food for a harmful invader and produces antibodies against it. Symptoms of a food allergy vary, and may include:

  • Stomach pains
  • Hives
  • Rashes
  • Diarrhea
  • Itchiness
  • Shortness of breath
  • A drop in blood pressure

The last two symptoms signal a condition known as anaphylaxis, which can be fatal if not quickly treated with injected epinephrine, the first line of defense against the condition.

About 15 million Americans, including approximately one in 13 children under the age of 18, suffer from food allergies, and the rate among children has risen about 50 percent since 1997. Scientists do not know why a given person develops a food allergy.

What's scary about food allergies is that they are unpredictable: A reaction may be mild one day, but severe the next time the offending food is eaten. A person can develop an allergy to any food at any time, but by far the most common allergens are:

  • Wheat
  • Soy
  • Fish
  • Shellfish
  • Peanuts
  • Tree nuts
  • Milk
  • Eggs

Together these eight substances account for about 90 percent of all food-allergic reactions.

Food Intolerance

One reason people confuse a food intolerance with a food allergy is that many of the digestive symptoms are the same. Since a food intolerance exhibits itself mainly in the gastrointestinal tract, sufferers typically experience side effects such as diarrhea, vomiting, gas, and bloat after eating the offending food. But unlike with an allergy, the immune system is not involved when you have a food intolerance. Another difference is that an intolerance may only manifest itself if a person consumes too much of a particular food, though what constitutes too much may vary from person to person. In contrast, allergy sufferers can have a reaction after eating or coming into contact with even a small amount of the allergen.

What causes food intolerance? Usually, it's the lack of an enzyme used to digest that particular food. The most common food intolerance in the U.S. is to milk and dairy, which affects about 10 percent of the population. Lactose-intolerant people typically lack lactase, an enzyme that helps to digest the lactose sugar in dairy products. "Another intolerance we are starting to see more of is fructose intolerance, where eating fruits can be equally troublesome because [the affected people] do not produce enough fructase, the enzyme that helps to digest fruit," says Laura Manning, a registered dietitian in the division of gastroenterology at Mount Sinai Hospital in New York.

Food Sensitivity

Many people assume that a food sensitivity is the same as an intolerance or an allergy, and use the terms interchangeably. However, according to the Institute of Food Technologists, a person with a food sensitivity may experience uncomfortable digestive symptoms at times after eating a particular food, while at other times will have no problems at all. The unpredictability of food sensitivities is baffling to experts. According to Manning, food sensitivities are often seen when food additives are used in order to extend a product's shelf life.

Laura Manning, RD, reviewed this article


Laura Manning, RD, division of gastroenterology at Mount Sinai Hospital in New York.