Allergy, intolerance or sensitivity: how to find out what's wrong with your food

Have you ever eaten something and, without really knowing why, you feel terrible?

You talk about it with your environment or even with professionals and the answer is usually the same: “it could be anything”.

The truth is that this discomfort may be due to a allergy, a intolerance or a food sensitivity. Although the symptoms sometimes resemble each other, the causes and solutions are completely different. That's why correctly identifying your case can save you years of discomfort, confusion and unnecessary restrictions.

In this article we explain clearly and directly how these three conditions differ, what signs to look out for and what you can do to find out the real cause of your digestive symptoms.

What is a food allergy?

A food allergy occurs when your immune system mistakenly identifies a food as a threat. This reaction is usually immediate or occurs within minutes and can range from mild symptoms to severe reactions that require urgent attention.

The most common symptoms include hives, itching, swelling of the lips or tongue, difficulty breathing and even anaphylaxis.

Some of the most common food allergies are nuts, shellfish, eggs and fish.

Diagnosis is made by skin tests or blood tests that measure specific IgE (immunoglobulin E) antibodies to certain foods.

What is a food intolerance?

Unlike allergy, the feeding intolerance does not involve the immune system. The problem here lies in digestion: the body cannot break down certain components of food properly.

Symptoms usually appear more gradually - minutes or hours after eating - and may include gas, bloating, diarrhoea, fatigue, a feeling of heaviness or even headache.

Common intolerances include lactose, fructose and SIBO (small intestinal bacterial overgrowth), which causes abnormal fermentation. To detect them, respiratory tests, breath tests or stool tests are used to see how your body reacts to these compounds.

What is food sensitivity?

The food sensitivity is less clear, but no less real. It occurs when the body reacts negatively to certain foods without an obvious allergy or intolerance.

Symptoms can be very varied: digestive, neurological (such as mental fog or migraines) or even cutaneous (such as rashes or acne). They are often subtle, cumulative and difficult to relate directly to a specific food.

In many cases, there is no definitive diagnostic test. Detection is usually based on observation: eliminating suspect foods from the diet and observing for improvement on reintroduction.

Features

It involves the immune system:
Allergy: ✅ Yes
Intolerance: ❌ No
Sensitivity: May be multifactorial

Time of appearance:
Allergy: Immediate (minutes)
Intolerance: Late (hours)
Sensitivity: Variable

Digestive symptoms:
Allergy: Sometimes
Intolerance: ✅ Frequent
Sensitivity: ✅ Frequent

Severe symptoms:
Allergy: ✅ Risk (anaphylaxis).
Intolerance: ❌ No
Sensitivity: ❌ Rarely

Clear diagnosis:
Allergy: ✅ Immunological tests
Intolerance: ✅ Respiratory tests
Sensitivity: ❌ Hard to detect

What to do if you suspect that food is bad for you?

• Start with a digestive diary.
  Write down what you eat, how you feel and when your symptoms appear. This record is very useful for identifying patterns and sharing them with professionals.
• Avoid self-diagnosis.
  Eliminating foods without proper guidance can be counterproductive and lead to nutritional deficiencies or further confusion.
• Take a test at home.
  There are tests you can do yourself, such as breath tests for SIBO, lactose or fructose. They are convenient, accurate and can give you a lot of information.
• Consult a professional.
  A digestologist or nutritionist specialising in gut health can help you interpret results and build a personalised and sustainable action plan.

Conclusion: Understanding your body is the first step

You are not overreacting if something feels wrong. Your body is trying to tell you something. You just need the right tools to interpret it.

With careful observation, a well-chosen test and the support of professionals, you can get back to enjoying food without fear, without discomfort... and without hesitation.

Find out which test you need to understand your symptoms → Start here.

References:

1. Colella M, Salvador Parisi CA. Food intolerance. Rev Allerg Mex [Internet]. 2023;70(4):265-8. Available at: http://dx.doi.org/10.29262/ram.v70i4.1337

2. Yu W, Freeland DMH, Nadeau KC. Food allergy: immune mechanisms, diagnosis and immunotherapy. Nat Rev Immunol [Internet]. 2016;16(12):751-65. Available at: http://dx.doi.org/10.1038/nri.2016.111

What are food sensitivities and how to identify them? [Internet]. [Nutriwhitesalud.com](http://nutriwhitesalud.com/). NutriWhite; 2023 [cited 2025 July 3]. Available from: https://www.nutriwhitesalud.com/blog/sensibilidades-alimentarias-como-diagnosticarlas