Could You Have a Food Sensitivity and Not Know It?

A food intolerance may not be so obvious at first—here's what to look for.

A woman sits on a bed holding her belly with food sensitivity symptoms. She has a food intolerance and it makes her ill. 

Updated on March 1, 2021.

If your skin breaks into a fiery, itchy rash, your tongue swells and breathing becomes difficult shortly after eating a shrimp cocktail, there’s a good possibility that you’re allergic to shellfish. Before you tear into a lobster tail or sink your teeth into a scallop, you should speak with your healthcare provider about a potential shellfish allergy.  

Although not all food allergies present in the same way, true food allergies have similar characteristics: They trigger an immune system response like a rash, trouble breathing or swelling of the mouth, cause exaggerated symptoms that can be severe and life threatening and appear within a few hours (or even a few minutes) after ingestion. 

In these instances, the specific allergen is easy to pinpoint. “If symptoms come on quickly after the food is ingested, it's easy to pick up and diagnose for most people,” says Mark Schecker, MD, and allergy and immunology specialist with Grand Strand Regional Medical Center in Myrtle Beach, South Carolina. 

But, not all unpleasant reactions to food are allergies. “When you use the term ‘food allergy,’ you're usually referring to something that's very specific,” Schecker says. “And there is a lot of misunderstanding about what food allergies are,” he adds. 

When it’s not an allergy 

So, if your body’s reaction to a specific food isn’t an allergy, what is it? Likely, it’s a food intolerance, or a sensitivity, to a certain food or group of foods, like wheat, dairy, soy, corn or fructose. 

Food intolerance is a condition in which the body finds it difficult to digest a certain food for a number of reasons: a lack of digestive enzymes, sensitivity to additives or a reaction to substances in the food. 

Unlike an allergy, an intolerance doesn’t typically cause an immune reaction. Instead, food intolerance symptoms tend to involve digestive system issues, which can include: 

  • Stomach cramps 
  • Nausea 
  • Vomiting 
  • Bloating
  • Heartburn
  • Diarrhea 

In some cases, certain foods are simply irritating to the digestive tract of some people. Others still experience symptoms unrelated to the digestive tract. Those with a food sensitivity might even experience symptoms like a cough, headache or runny nose. And unlike an allergy, signs of an intolerance are usually less serious and more easily ignored.  

The symptoms aren’t the only variable between an allergy and an intolerance. The timing of symptoms differs, as well. “Symptoms that appear after two hours of eating a food are usually not from allergy,” Dr. Schecker says. 

The onset of food sensitivity symptoms occurs several hours, or even days, after ingestion, often making the source of the discomfort hard to diagnose. You could be experiencing signs of sensitivity without realizing it. 

Different still from a wheat allergy and intolerance is an autoimmune disorder, like celiac disease, in which the ingestion of gluten—a protein in wheat—can damage the lining of the small intestine. Celiac disease does cause an immune response, but it’s not the same as that of a true allergy. 

Symptoms of celiac disease appear between 48 and 72 hours after ingestion, and include abdominal bloating and pain, diarrhea, vomiting, constipation, heartburn, fatigue, headaches and joint pain. 

A difficult diagnosis 

Sometimes, food allergies can be diagnosed by symptoms alone. Other times, allergies are easily diagnosed with skin and blood tests. 

Food intolerances, on the other hand, are a bit more difficult. “Other sensitivities to foods are much more difficult to diagnose because we don't have diagnostic testing,” Schecker says. 

Without a test to diagnose food intolerances, healthcare providers must look to other options, like eliminating possible triggers from a person’s diet. 

“Sometimes, the only way to determine an intolerance is to eliminate certain foods from the diet, and try to gradually reintroduce one at a time,” Schecker says. 

A food diary may also be helpful. Logging the food you eat along with subsequent symptoms each day, over a period of time, may help narrow down some common factors.  

Finding a solution 

After your healthcare provider has successfully diagnosed your sensitivity, you will likely work together to determine the best way to control or avoid food intolerance symptoms. 

Treating food intolerance focuses on avoiding or limiting intake of the troublesome food. Small amounts of the particular food may not cause a reaction, in which case eliminating the food entirely may not be necessary. 

In instances where enzymes, responsible for breaking down certain foods, are deficient, some over-the-counter medications can be taken before a meal. Lactase enzymes, for example, may help reduce the intolerant effects of dairy.

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