How to Tell if You Have a Food Allergy or Intolerance

If you’ve ever had an adverse reaction to something you’ve eaten or experience ongoing digestive issues, you may wonder if you have a food allergy, intolerance or sensitivity.

Though these terms are often used interchangeably, the differences between them are significant.

Food Allergy

A food allergy occurs when the body’s immune system reacts to a protein in food, treating it as a threat. Antibodies called immunoglobulin E (IgE) respond by signaling for the release of a chemical called histamine into your bloodstream. This chemical causes allergy symptoms like sneezing and runny nose, and can lead to serious, even life-threatening, reactions. For some people, even trace exposure—through eating, touching, or inhaling—may cause symptoms.

In the U.S., food allergies affect around eight percent of children and nearly 11 percent of adults. The most common culprits are milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, soybeans, and sesame.

Symptoms

Symptoms of food allergy typically appear within minutes to two hours after exposure and can include hives, swelling of the face, tongue, or lips, vomiting, diarrhea, and difficulty breathing. In severe cases, food allergies can lead to anaphylaxis, which involves a range of potentially life-threatening reactions across body systems.

Diagnosis

Diagnosis relies heavily on patient history, according to John Leung, MD, AGAF, FACAAI, adjunct associate professor at the Friedman School and founder of Boston Specialists. Skin-prick tests and blood tests measuring food-specific IgE levels can support a diagnosis. Leung cautions against over-the-counter testing, saying, “many online direct-to-consumer allergy tests are costly and lack scientific validity.”

Treatment

Allergens must be strictly avoided. Because accidental exposure can happen, having an emergency plan and access to epinephrine (such as an EpiPen) is essential. Newer treatments like oral immunotherapy (desensitization) and FDA-approved medication are helping some patients reduce the risk of severe reactions.

Food Intolerance

Food intolerance occurs when the digestive system has difficulty breaking down certain foods. Unlike a food allergy, an intolerance does not involve the immune system and is not life-threatening. Common intolerances include lactose intolerance (the inability to digest the dairy sugar lactose due to low levels of the enzyme lactase in the intestine) and dietary fructose intolerance (difficulty absorbing fructose, a type of sugar found in fruits, vegetables, and most caloric sweeteners). Some people report an intolerance to the protein gluten. Research suggests that fructans (carbohydrates found in many of the same foods as gluten), rather than gluten, may be the trigger for many.

Symptoms and Diagnosis

Symptoms of food intolerance typically include gas, diarrhea, bloating, and/or stomach pain that generally appear within a few hours after eating.

Lactose and fructose intolerance can be diagnosed by a medical professional with a test that measures changes in the amount of hydrogen and methane in your breath before and after you consume the trigger food. Tracking symptoms with a food diary or using an elimination dietary pattern under medical supervision are common strategies for identifying other intolerances.

Treatment

Most people can tolerate small amounts of the problematic food without serious distress, but may need to change their diet to limit or eliminate problem foods. Over-the-counter medicines like antacids or antidiarrheals may help symptoms. People with lactose intolerance can consume lactose-free dairy products or use over-the-counter lactase enzymes.

Food Sensitivity

The term “food sensitivity” is not a medically recognized term. People report a variety of symptoms, including gastrointestinal discomfort, joint pain, fatigue, rashes, and/or brain fog that they associate with specific foods or food components. Although there are a number of programs on the market claiming to diagnose food sensitivities, these are not supported by rigorous science.

If you are experiencing symptoms you believe are connected to the foods you eat, it’s important to get professional help. “Many people delay seeing a doctor because social media suggests their issue is just a food sensitivity or intolerance,” Leung cautions. “They try eliminating foods at home without success, sometimes postponing a proper diagnosis for a year or two. Self-diagnosis and self-treatment can cause people to miss serious medical conditions that require professional attention.”

This article originally appeared in the Tufts Health & Nutrition Letter, published each month by the Friedman School of Nutrition Science and Policy.