Understanding food allergies, intolerances, and sensitivities

There are three types of reactions people may have to foods: allergies, intolerance, and sensitivity. It’s not unusual to see some of these terms used interchangably, and most people aren’t aware of the differences between them, but the differences are important.

Allergies and intolerance

Food allergies are when your body perceives a food as a dangerous intruder and mobilizes the immune system (IgE, specifically) to fight it. Reactions may vary from a skin rash to one’s airways suddenly swelling closed, which can quickly become life-threatening.

Food intolerance means that your body has difficulty digesting certain foods. Symptoms are usually digestive problems such as bloating or diarrhea, but may also include respiratory symptoms or headaches.

This chart further explains the differences between these two:

Other common food allergies not listed by the chart include wheat and soybeans. Less common allergens include corn, gelatin, various meats, seeds (sesame, sunflower, and poppy being the most common) and certain spices.



Food sensitivity is controversial in some quarters because it doesn’t always show up in common lab tests, and doctors tend to mistrust anything they can’t measure.

It’s similar to allergies in that it involves the immune system (but the reaction is usually less violent or and not usually life-threatening), but it’s similar to intolerance in that reactions to food are usually delayed and may be in proportion to the amount ingested. While not immediately life-threatening, it may do damage to the body. For example, in a person with celiac disease, the reaction to gluten may cause damage to the small intestine. (Learn more about celiac here.)

Some people who are merely sensitive have found that if they remove all offending foods from their diet for a time (months or years), their system heals to the point where they can again enjoy those foods in moderate quantities.

Symptoms may include:

  • Bloating or irregular digestion
  • Skin rashes of any kind, including adult acne
  • Runny or stuffy nose
  • Muscle and joint pain
  • Depression and mood swings
  • Foggy head; difficulty with mental focus
  • Autoimmune diseases (such as Graves’ Disease, Hashimoto’s, lupus, MS, rheumatoid arthritis, and more)

Foods don’t cause the autoimmune disease — which often have a genetic link — but food intolerances can add fuel to the symptoms. A common saying is, “Genetics loads the gun, but lifestyle/environment pulls the trigger.”

Food sensitivities vary from person to person. Which foods are the main cause of food sensitivity is the topic of much debate! Three different websites yielded three different lists:

  • Wheat/gluten, corn, soy, dairy/milk, eggs
  • Cow’s milk, eggs, beans, nuts, cereals/grains
  • Nightshades, eggs, nuts, seeds, gluten, grains, legumes, dairy



Food allergies and intolerances are well-known and agreed upon in the medical community, and so finding reliable information about them is not difficult. Food sensitivities, however, are more controversial, and harder to diagnose. This doesn’t mean that they’re not real: just that science is still working out the kinks in the theory.


If you think you may have food sensitivities, here are some books to explore:

It Starts With Food – This book contains some “science-y stuff” (the authors’ term), but leans heavily toward easy-to-read. It explains the “what” and a little of the “why” behind the Paleo diet*, which is an elimination diet that has helped many people with food-related health issues.

Also, see my review of Digestive Health with Real Food. This is the most thorough treatment of food sensitivity I’ve read, emphasizing that there is no one-size-fits-all diet.

*I don’t think the Paleo diet is something everyone needs to adhere to strictly, but the proof is in people: Paleo does seem to work for a lot of people with the types of ailments that have exploded in America in the last few decades. It eliminates some of the items that show up on every expert’s food sensitivity list — grains, soy, beans/legumes, and dairy. It does allow eggs, though, which are a pretty common allergen, so I don’t see it as very scientific.


American Academy of Allergy, Asthma and Immunology  – Definition of allergies/intolerance

American College of Allergy Asthma and Immunology – Detailed info on food allergies

Today’s Dietician – Definition of allergies/intolerance

Mayo Clinic – Difference between a food intolerance and food allergy

Chris Kresser – Gluten sensitivity

Allergy UK – Common food intolerances

Medical News Today – Common causes of food intolerances

Medline Plus – Definition of celiac disease

Very Well article: An overview of celiac disease


I’m not a doctor, nutritionist, or any other health professional. You should always check stuff out for yourself!

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