Food Reactions: Allergy, Intolerance or Sensitivity?


Written by

An unpleasant reaction to a particular food is really common. Perhaps you’ll experience immediate symptoms, but most often symptoms arise after some hours, or even days. If you think you react to certain foods, unless you do react immediately, it can be difficult to pin down exactly which foods. Understanding more about how these reactions occur can help identify the problem and gives pointers as to what to do about it.

Allergy vs Intolerance vs Sensitivity

Food Allergy

A true food allergy is a well-defined condition and refers to a particular type of immune reaction that involves a specific type of antibody (called IgE) against a specific food.1–4

The terms food sensitivity and food intolerance are often used interchangeably, or with varying definitions.

Food Intolerance

Commonly this doesn’t involve an immune reaction and is considered to be due to an inability to digest a particular food.5 For example, in the case of lactose intolerance, the problem is a lack of the enzyme required to break down lactose into a form that can be absorbed by the body.

Food Sensitivity

This may refer to a different kind of immune reaction that uses different antibodies, such as IgG or IgA, for example in coeliac disease.

What are the differences?

Food allergy
Food intolerance
Food sensitivity
IgE antibodies to
Unable to digest
certain foods
IgG or IgA antibodies to foods
Usually comes on suddenly.
May happen hours or days after eating
May happen hours or days after eating
Small amount of food can trigger.
Happens every time you eat the
May only happen when you eat a lot of the food or often.May only happen when you eat a lot of the food
Can be life-threateningIs not life-threateningIs not life-threatening
Symptoms include:

Stomach pain
Rash, hives, or itchy skin
Shortness of breath
Chest pain
Sudden drop in blood pressure
Trouble swallowing or breathing 
Symptoms include:

Stomach pain
Gas, cramps, or bloating
Irritability or nervousness
Skin problems such as eczema
Joint pain.
Symptoms include:

Gas, cramps, or bloating
Irritability or nervousness
Skin problems such as eczema
Brain fog
Mood changes
Runny nose
Weight gain/loss
Sleep problems
Common foods:

Tree nuts
Milk (protein)
Common foods:

Milk (lactose)
Food additives
Foods high in histamine
Foods high in salicylates
Foods high in fructose
Common foods:

“Nightshades” (tomatoes, aubergine, peppers, potatoes)
Onions, leeks etc

Can I get tested for an allergy, intolerance or sensitivity?

Food Allergy Testing

This can be done by your doctor with a blood test measuring IgE antibodies or skin tests, which are considered more accurate.6 If you have a diagnosed or suspected allergy, you should avoid that food completely.

Food Intolerance and Sensitivity Testing

(often simply called food intolerance testing)

This is more complex. Well-established testing exists for some forms of food intolerance and food sensitivities, such as lactose intolerance or coeliac disease, which again your doctor will be able to organise.7,8

While it is possible to test for IgG antibodies to specific foods, these tests are less reliable. This is because you can have the antibodies and not have a food sensitivity, or you can have a sensitivity but not have the antibodies. This happens because you could be sensitive for a reason other than there being an immune reaction.9 

Alternatives to Formal Testing

An alternative way to test for food sensitivity or intolerance is an elimination diet. This is where you eliminate certain foods for a period of time then reintroduce them while monitoring symptoms. This process needs to be done in a very controlled manner so as to be certain which foods are causing you problems.

When it comes to the re-introduction of foods, it is important to introduce foods slowly and leaving plenty of time for a reaction to develop. This is as food intolerances and sensitivities can take hours or even days to become apparent and may also depend on the amount of food consumed. All of this must happen while keeping other foods in your diet restricted to those you are certain are “safe” for you.


If you are struggling to identify which foods are a problem for you, consider working with a nutritional therapist or other professional who is experienced in the process who can help you to identify your problem foods safely.10–12  

Further reading

1. Sampson HA. Historical Background, Definitions and Differential Diagnosis. In: Chemical Immunology and Allergy. Vol 101. Karger Publishers; 2015:1-7. doi:10.1159/000371644.

2. Ballmer-Weber BK. Food Allergy in Adolescence and Adulthood. In: Chemical Immunology and Allergy. Vol 101. ; 2015:51-58. doi:10.1159/000371669.

3. Heine RG. Gastrointestinal Food Allergies. In: Chemical Immunology and Allergy. Vol 101. ; 2015:171-180. doi:10.1159/000371700.

4. Valenta R, Hochwallner H, Linhart B, Pahr S. Food allergies: the basics. Gastroenterology. 2015;148(6):1120-31.e4. doi:10.1053/j.gastro.2015.02.006.

5. David TJ. Food intolerance. In: Food Allergy: Molecular Basis and Clinical Practice. ; 2010. doi:10.1016/B0-12-226694-3/00137-X.

6. Eigenmann PA. Do we still need oral food challenges for the diagnosis of food allergy? Pediatr Allergy Immunol. 2018;29(3):239-242. doi:10.1111/pai.12845.

7. Elli L, Branchi F, Tomba C, et al. Diagnosis of gluten related disorders: Celiac disease, wheat allergy and non-celiac gluten sensitivity. World J Gastroenterol. 2017;21(23):7110–7119. doi:10.3748/wjg.v21.i23.7110.

8. Di Rienzo T, D’Angelo G, D’Aversa F, et al. Lactose intolerance: from diagnosis to correct management. Eur Rev Med Pharmacol Sci. 2013;17 Suppl 2:18-25.

9. Lavine E. Blood testing for sensitivity, allergy or intolerance to food. Can Med Assoc J. 2012;184(6):666-668. doi:10.1503/CMAJ.110026.

10. Tuck C, Barrett J. Re-challenging FODMAPs: the low FODMAP diet phase two. J Gastroenterol Hepatol. 2017;32:11-15. doi:10.1111/jgh.13687.

11. Barrett JS. How to institute the low-FODMAP diet. J Gastroenterol Hepatol. 2017;32:8-10. doi:10.1111/jgh.13686.

12. Lim H-S, Kim S-K, Hong S-J. Food Elimination Diet and Nutritional Deficiency in Patients with Inflammatory Bowel Disease. Clin Nutr Res. 2018;7(1):48-55. doi:10.7762/cnr.2018.7.1.48.