Since a fair portion of my time on this blog is dedicated to salicylate sensitivity, I thought it prudent to distinguish between food sensitivity and food allergy; two very different biological responses. The key difference between the two is that an allergy involves the immune system whereas a food sensitivity occurs without an immune basis. Unfortunately, the two terms are often used interchangeably, and this misunderstanding can lead to unwarranted stress and response on the sufferers part, especially when Dr Google is involved!

In this blog post I will seek to define both food sensitivity and food allergy, and list common symptoms associated with the two along with diagnostic differences.

Difference between an allergy and food sensitivity (e.g. salicylate sensitivity)

Salicylates are a group of chemicals derived from salicylic acid found naturally in plant foods and in synthetic forms such as aspirin (acetylsalicylic acid) and food preservatives.

Research shows that about 20% of adults with asthma (3) and more than half of people with food-induced itchy rashes, headaches, migraines or irritable bowel symptoms, and children with behaviour problems may be sensitive to salicylates (4)(5).

While both a food sensitivity and a food allergy result in unwarranted reactions, they do not involve the same processes.

Food Allergy

An allergy is when the immune system isn’t able to distinguish between potentially dangerous and innocuous molecules. When a food allergy occurs, the immune system responds inappropriately to a specific protein in a food  (allergen) that isn’t intrinsically harmful. Food allergy typically involves only a few foods such as egg, peanut, milk, soya, fish and wheat.

Symptoms don’t tend to arise upon first exposure of the allergen. Instead, an allergic reaction requires an initial exposure to the allergen whereby large quantities of IgE antibodies specific to the allergen are produced. The IgE antibodies attach to mast cells, ‘priming’ them towards the allergen. With any subsequent exposure, the allergen binds to antibodies on the mast cell, releasing histamine from the mast cell which causes an inflammatory response / allergic symptoms (e.g. histamine causes inflammation which triggers capillary permeability which leads to fluid releasing into tissues which leads to swelling which leads to compression of nerves which leads to pain).

Symptoms can appear instantaneously or over a couple of hours, and can range from mild to severe, the most extreme being anaphylactic shock which can involve difficulty breathing, swelling of the throat, vomiting and fainting, possibly leading to death if medical intervention is not obtained.

There are also non-IgE mediated food allergies that involve activation of the immune system but occur without IgE antibodies. Reactions tend to occur in the GI tract (e.g. delayed vomiting/diarrhea, abdominal pain, bloating), however, can include airway issues, delayed onset of eczema and irritably. Symptoms associated with non-IgE allergies aren’t generally immediate but instead present 2-24 hours after eating the culprit food (e.g. cow’s milk, soy protein and/or wheat).

It is not known exactly why some people suffer from allergies and others don’t, however there’s evidence to suggest that genetics and environmental factors are at play (6). 

Food Sensitivity

Not to be confused with an allergy, food sensitivity does not involve the immune system. Chemicals, such as salicylates, are digested and absorbed normally, however, they can irritate nerve endings in different parts of the body leading to a reaction in sensitive individuals. Symptoms are thought to result from an overproduction of leukotrienes, inflammatory mediators that are best known for their role in the development of asthma, rheumatoid arthritis and inflammatory bowel disease (1).

Food sensitivities can affect one or more systems (e.g. skin, airways, gastrointestinal, nervous system) and chemical sensitivity appears to have a genetic component, usually affecting the same system across generations (2). Onset of symptoms usually occur about half an hour after eating or drinking, however, it’s not uncommon for symptoms to appear up to two or three days later.

Also, it’s worth mentioning that the terms food sensitivity and food intolerance, while often used interchangeably, actually have different meanings. Food intolerance refers mostly to the inability to process or break down a compound such as lactose or gluten; the food or chemical is not tolerated. Food/chemical intolerance (such as aspirin intolerance) doesn’t trigger an immune response as it involves a reaction to a chemical compound, not a protein. However, those with a food/chemical intolerance, when triggered, can experience a histamine reaction which can cause symptoms akin to an allergic reaction. Food sensitivity, on the other hand, is a reaction to a stimulus that is dependent on dosage; a little can be fine, but too much and you have a reaction. Food sensitivity also doesn’t always involve a histamine reaction and thus symptoms in this case, though unpleasant, aren’t life-threatening.

Life-threatening vs life-altering

Another distinction between the two is that food allergies can be life-threatening, whereas food sensitivities, while unpleasant, do not generally result in an untimely death (note: benzoates and sulfates may cause anaphylaxis). Somewhat of a relief, I’m sure, to those diagnosed with a food sensitivity.

Reactions in people with food sensitivities are usually dose dependent (overshoots a personal threshold) and such people can often eat small amounts of the culprit foods without too much trouble. However in a person that suffers from an allergy, even a tiny amount of the substance they are allergic to can result in a severe reaction.

Summary

Common symptoms associated with food sensitivity and allergy

As you can see, symptoms of food allergy and food sensitivity can overlap, making it difficult to distinguish between the two. In order to ascertain whether a person has a food intolerance or an allergy, careful investigation and/or relevant testing by a trained professional is recommended in order to reach an accurate diagnosis.

Diagnostic differences between food sensitivity and allergies

Food allergy

Testing for food allergy generally involves careful examination by healthcare professionals as well as evidence-based testing. Such evidence-based tests include the detection of IgE antibodies for the suspected food/substance through skin prick and/or blood tests, measuring IgE-mediated cellular responses and food allergen challenges which involve a person ingesting a suspected allergen in the presence of medical professionals to confirm or exclude a food allergy (7). Non-IgE mediated food allergies, however, can only be diagnosed via an elimination diet and food challenges, preferably led by a dieteitian.

Food sensitivity

The elimination diet is currently the only useful diagnostic tool for investigating food sensitivity. The diet, developed by the Royal Prince Alfred Hospital (RPAH) involves cutting down on a range of food chemicals that are known to cause symptoms in some people. After a period of time, foods containing high doses of the suspect chemical (e.g. salicylates) are reintroduced to see if reactions ensue, often days after the initial exposure.

Due to its restrictive nature, the elimination diet should only be applied short-term so as not to starve the body of essential nutrients and undertaken under the guidance of an accredited dietitian​.

Conclusion

Food sensitivity and food allergy both elicit uncomfortable and undesired reactions. What they don’t share however, is the way in which said reactions materialise. Being able to distinguish between the two is vital, not only for effective communication, diagnosis and treatment, but to ensure individuals are left feeling fully versed on their condition.

Brigid xx

References

(1) Szczeklik A, Sanak M, Nizankowska-Mogilnicka E, Kiełbasa B. Aspirin intolerance and the cyclooxygenase-leukotriene pathways. Curr Opin Pulm Med. 2004 Jan;10(1):51-6. doi: 10.1097/00063198-200401000-00009. PMID: 14749606.

(2) Swain, A., Soutter, V, & Loblay, R. (2011). RPAH Elimination Diet Handbook with food and shopping guide. Australia: Allergy Unit, Royal Prince Alfred Hospital.

(3) Jenkins C, Costello J, Hodge L. Systematic review of prevalence of aspirin induced asthma and its implications for clinical practice. BMJ. 2004 Feb 21;328(7437):434. doi: 10.1136/bmj.328.7437.434. PMID: 14976098; PMCID: PMC344260.

(4) Loblay RH, Swain AR. ‘Food intolerance’. In Wahlqvist ML, Truswell AS, Recent Advances in Clinical Nutrition. London: John Libbey, 1986, pages 169-177.

(5) Swain A, Soutter V, Loblay R, Truswell AS. Salicylates, oligoantigenic diets, and behaviour. Lancet 1985;2(8445):41-2.

(6) Ortiz, Romina A, and Kathleen C Barnes. “Genetics of allergic diseases.” Immunology and allergy clinics of North America vol. 35,1 (2015): 19-44. doi:10.1016/j.iac.2014.09.014

(7) Valenta, Rudolf et al. “Food allergies: the basics.” Gastroenterology vol. 148,6 (2015): 1120-31.e4. doi:10.1053/j.gastro.2015.02.006