Food Allergies or Sensitivity? Brian Lacy, MD, Explains

Dr Lacy reviews the diagnostic signs of true food allergies, including anaphylaxis, versus food sensitivities that may cause gastric symptoms.

Brian Lacy, MD, is a professor of medicine at Mayo Clinic-Florida in Jacksonville, Florida.

Food Allergy Versus Food Sensitivity: Clinical Assessment at ACG 2026

• Brian Lacy, MD, estimated that true food allergy affects 3%–10%. At the October 2026 ACG meeting, he emphasized that food-related symptoms alone do not establish the diagnosis.
• Assessment of food allergy involves a reproducible reaction after eating a specific food, with findings such as swelling, difficulty swallowing, or shortness of breath, raises concern. History and examination are central; allergist-directed skin-prick testing or serum IgE may support the diagnosis.
• For confirmed food allergy, Lacy advised avoiding the identified food, seeing an allergist, carrying an epinephrine autoinjector, and wearing a medical alert bracelet.

Welcome from Nashville, Tennessee. I'm Brian Lacy, a professor of medicine at the Mayo Clinic in Jacksonville, Florida at the ACG annual meeting. For the next couple of minutes, I'd like to discuss my approach to the patient with concerns over a possible food allergy versus a food sensitivity. And as a gastroenterologist, I'm asked to see these patients all the time because many patients believe that symptoms related to food ingestion represent a food allergy.

So let's set the stage a little bit. And the first is, how common are food allergies? We used to believe that food allergies were actually quite uncommon, that they were rare, but in fact, that's not true. We estimate that the prevalence of a true food allergy, it ranges from about 3 to 10% in American adults. So it depends on which study you read, but that's much higher than was previously quoted.

And there are a lot of misconceptions and myths about food allergies, and I want to highlight that first before we discuss diagnosis and treatment. And part of that misconception is that food allergies are uncommon, although we've just learned that actually they're much more common than before. The second thing is that food allergies, as a myth, is that you can identify them by symptoms alone, and that's not true at all. Oftentimes, some testing to support the diagnosis is necessary. The next misconception is that if you just read the label about a food, you'll be able to identify a food allergy. That too is untrue. And also there's a big misconception about the difference between food allergies and food sensitivities, which are much more common.

So let's talk about symptoms related to a food allergy and how you might make that diagnosis. So it's important to understand the pathophysiology of a food allergy, and that's really critically important. So it's an immune mediated event that's reproducible. So one of the problems with patients reporting symptoms after eating is that it may not always represent what they just ate. It may be something from maybe before. It may be a combination of foods, but a true food allergy means that every time you eat the food, you have symptoms. And those symptoms typically, because it's an immune mediated event, increase over time. And that's important because we need to recognize a true food allergy, which could be a life-threatening event.

So what are the symptoms that are representative, characteristic of a true food allergy? We think about periorbital edema or swelling, swelling of the mouth or tongue. We think about difficulty swallowing. We think about rhinorrhea and nasal congestion. As symptoms progress, people may become short of breath. And then if you truly are developing an anaphylactic, a life-threatening, reaction, this is a true hypersensitivity reaction that can lead to death. There may be changes in blood pressure, hypotension, cardiovascular collapse, and even death. And that's why it's critical to distinguish a true food allergy where patients should be wearing a bracelet. They should be carrying an EpiPen from somebody with a food sensitivity.

All right, so let's think about common foods that can cause a food allergy. And in adults, shellfish about 2%. We think about sesame seeds, we think about nuts, including peanuts, milk, eggs, and shellfish. So some of those are the most common food allergies with prevalence rates of shellfish for about 2% to milk allergies in adults about 0.5% or even less. So how to make that diagnosis. So one is taking that great history. Again, symptoms should be reproducible with those characteristic findings of periorbital edema, difficulty swallowing, rhinorrhea, and maybe shortness of breath.

Number two, testing is supportive. So I caution all my patients, beware about unvalidated tests. You can't make a food allergy diagnosis with a stool sample or a fingernail sample or a hair sample. You can't make that diagnosis by testing the skin or measuring pulse. All that is absolutely just nonsense. It's really snake oil. So you can have supportive testing by having somebody see an allergist and do a skin prick test. And if you see an immediate reaction with a wheal greater than 3 millimeters in size, that is supportive of the diagnosis. And in patients with symptoms suggestive of food allergy, you could check a serum immunoglobulin E, and if values are medium or very high, that again supports it, but it's all supportive. It's the history, the exam that's most consistent and most diagnostic of a food allergy. So let's think about treatment. So obviously the easy treatment is avoiding those foods once you've identified them. As I've mentioned, with true food allergies, you should wear a medic alert bracelet and you should be carrying EpiPen, but there are other new things coming down the pike.

So as an example, you can start giving patients small amounts of that food allergen to help develop tolerance. So we can do that with sublingual amounts of small amounts of the food that they are allergic to or subcutaneous injections. There is also now an FDA approved medication, Xolair, which could be used for food allergies. And there's actually an FDA approved medication for adolescents for those with peanut allergies. So the field is growing and expanding as we become a little bit more aware of this.

And as we wind down, I just want to touch on why are food allergies a little bit more prevalent than in the past? Because patients are going to ask you, "Why do I have this food allergy now as an adult?" So there are a couple of theories. One is what we call the clean hypothesis. Many of us, our houses, our apartments, our condos are much cleaner now than 50 or 100 years ago. Kids are not outside, they're not playing in the dirt, they're not playing in the barn, they don't have animals. And sometimes being too clean means that you're not seeing things in the immune system you used to see before and now you are intolerant to that, that immune reaction. There's also a theory that low vitamin D could be playing a role. And also the fact that we are probably eating foods now that are so processed, this ultra processed food concept or processed food concept, and therefore that changes the gut microbiome. And so now when we ingest some foods, our body doesn't quite recognize them as normal and it recognizes as abnormal and therefore you induce this immune response.

So as we wind down here, the teaching points are kind of keep your radar screen up when you hear about food related symptoms, consider a food allergy even new in adults. It's a little bit more common in patients with atopic symptoms, asthma, eczema, seasonal allergies or latex allergy. Remember the history is key, testing is supportive, and certainly if you have somebody with a true food allergy, make sure they see an allergist, make sure they have a EpiPen and keep them away from those foods. So from Nashville, Tennessee at the ACG meeting in October 2026, I'm Brian Lacy at the Mayo Clinic in Jacksonville, Florida. Thank you for joining us today.