Two very different reactions to food — one involves your immune system, the other your digestion. Here’s how to tell them apart, and why allergy worries always belong with your GP.

Allergies: An Immune System Response

A food allergy is an abnormal immune system reaction. It happens when your body mistakes a harmless food protein for a threat. Your immune system makes antibodies called IgE, which attach to cells in your nose, throat, lungs, stomach, and skin. The next time you eat that food, the allergen binds to those IgE antibodies and triggers the release of chemicals like histamine, which causes symptoms quickly.

Food allergies can be serious. They may cause breathing difficulties, swelling of the throat, widespread rashes, or anaphylaxis — a sudden, life-threatening reaction that needs emergency help. Some people carry an adrenaline auto-injector because of this risk. Allergic reactions usually appear within minutes to about two hours of eating the food.

This matters for one simple reason: allergy is a medical matter, and it is not what our test looks at. If you think you might have a food allergy — even a mild one — please see your GP or ask to be referred to an allergy specialist. They can carry out proper allergy testing, such as skin prick tests or IgE blood tests, to confirm what is going on. Our hair screening does not, and cannot, do this.

Intolerances: A Digestive System Issue

A food intolerance is different. It happens when your digestive system struggles to break down or process certain foods — often because you are short of a particular enzyme, or because you are sensitive to something in the food. Unlike an allergy, an intolerance does not involve your immune system and cannot cause anaphylaxis. It will not put your life at risk, but it can leave you feeling rough.

People often describe bloating, wind, stomach pain, nausea, or changes in their bowel habits. Intolerances are frequently dose-dependent: a small amount of a food might sit fine, while a larger portion brings on symptoms. Reactions can also be slow, turning up hours or even a day or two after eating the food, which makes the culprit much harder to spot than with an allergy.

Because an intolerance is about digestion rather than immunity, the most practical way to explore it is an elimination diet — removing a suspected food for a while, then reintroducing it on its own while you keep track of how you feel.

How Hair Screening Can Suggest Foods Worth Exploring

IntoleranceLab screens a hair sample across 700+ items (350 foods & drinks + 350 non-food items), and gives you back a shortlist of foods that might be worth exploring through an elimination diet. We want to be very plain about what this is and is not. It is not an allergy test. It does not measure IgE antibodies, it cannot tell you anything about allergy or anaphylaxis risk, and it does not diagnose anything.

Think of it instead as a starting point — a way to narrow the field when you suspect certain foods may be linked to digestive discomfort or other niggles but you don’t know where to begin. The results simply hand you a shorter list of foods to experiment with, so you are not removing things from your diet completely at random. From there, the real work is yours: you remove those foods for six weeks, then reintroduce them carefully one at a time while noting how you feel.

We will not promise that this will change your symptoms — everyone’s body is different and responses vary a lot. What we can offer is a quicker, less overwhelming way to decide which foods to focus on first. Your results arrive within 3 days of your sample reaching our UK lab.

The Elimination Diet: A Careful, Step-by-Step Approach

Once you have a shortlist of foods to look at, an elimination diet is the most practical way to learn something useful about your own body. You remove the suspected foods completely for six weeks, keeping a simple diary of your symptoms and how you feel day to day — start the diary on day one, because memory is unreliable and patterns hide in the gaps. During this settling-in period you give your body a chance to calm down, and you can watch for any change.

After those six weeks, you reintroduce foods one at a time, leaving three to five days between each, and note whether anything comes back. This slow, methodical approach is what reveals which specific foods, if any, seem to be linked to how you feel. Some people find only one or two foods bother them; others learn they can manage a small amount but not a big portion.

It takes patience and a bit of record-keeping, but the pay-off is personal observations about your own body rather than guesswork — and you can take those observations to your GP or a registered dietitian if you want extra guidance. The six-week core plan matters for one more practical reason: it is exactly what our 90-day money-back guarantee asks you to follow, so running it properly keeps you covered either way.

Allergies Are a Medical Matter — When to See Your GP

If you ever have a sudden, severe reaction after eating — difficulty breathing, swelling of the throat, a widespread rash, or feeling faint and dizzy — regard it as an emergency. Contact your GP straight away, or call 999 if symptoms are severe or getting worse quickly.

If you suspect a food allergy of any kind, even a mild one, ask your GP for a referral to an allergy specialist. They can carry out proper allergy testing, such as skin prick tests or IgE blood tests, to confirm what is happening. This really matters, because a confirmed allergy changes how you handle food day to day — you may need to carry emergency medication and take care over cross-contamination.

None of this is something a hair screening can tell you, and it is not something you should try to work out with an elimination diet. Allergy belongs firmly with a medical professional. Intolerances, on the other hand, are usually explored with the support of your GP or a registered dietitian, using elimination and symptom tracking rather than any single test.

What Changes When You Remove a Food

When you stop eating a food your body doesn’t get on with, symptoms often ease or fade — but it’s worth being clear about why. Any change comes from removing the food, not from the test. The test only ever points you toward foods to try removing; the elimination process is where anything actually shifts. As your digestive system settles, some people notice less bloating and a bit more comfort day to day.

Once you’ve spotted which foods seem to be linked to how you feel, you can make your own informed choices: avoid a food entirely, keep to smaller portions, or simply keep an eye on it. Some intolerances ease if you give a food a long rest; others stick around. Individual responses vary a great deal, which is exactly why working it out for yourself through elimination tends to be more useful than any blanket rule.

The screening is the starting point; removing and reintroducing foods is where the learning happens. And if your symptoms are persistent, severe, or worrying, please don’t sit with it alone — speak to your GP so anything more serious can be ruled out.

If you’d like a focused place to begin, that’s the one honest job our screening does: a starting shortlist drawn from 700+ items for £49, your report within 3 days of your sample arriving, and a 90-day money-back guarantee — no pressure either way.

At a glance

Being straight with you

• IntoleranceLab screens a hair sample across 700+ items (350 foods & drinks + 350 non-food items) and gives you a shortlist of foods worth exploring through an elimination diet
• It gives you a personalised starting shortlist — a non-invasive, quick option
• Results arrive within 3 days of your sample reaching our UK lab
• Any symptom change comes from the elimination process — from removing a food — not from the test itself
• It is designed to support the elimination-and-reintroduction approach by helping you decide which foods to focus on first
• Backed by a 90-day money-back guarantee — conditions disclosed plainly: a 6-week elimination plan and a simple food diary

• NOT an allergy test — it does not detect IgE allergies or say anything about anaphylaxis risk
• NOT a medical diagnosis — results suggest foods to explore, nothing more
• NOT a replacement for seeing your GP if you suspect a food allergy or have severe reactions
• NOT able to diagnose coeliac disease, lactose intolerance, or any medical condition
• NOT a cure or treatment — it is an exploration tool to support an elimination diet
• NOT a promise that removing any food will change how you feel — responses are individual (that’s exactly why the money-back guarantee exists)

Common questions

Can IntoleranceLab test for food allergies?

No. IntoleranceLab does not test for IgE food allergies, and it cannot tell you anything about allergy or anaphylaxis risk. If you think you have a food allergy — especially if you have ever had sudden swelling, breathing difficulties, or another severe reaction — please see your GP or ask for a referral to an allergy specialist. They can carry out proper allergy testing, such as skin prick tests or blood tests.

IntoleranceLab cannot diagnose anything — so what does it actually do?

Exactly that — it is not a diagnosis, and we won’t pretend otherwise. IntoleranceLab screens your hair sample across 700+ items (350 foods & drinks + 350 non-food items) and gives you a personalised shortlist of foods worth exploring first through an elimination diet. Any improvement you notice comes from the elimination process itself — the report simply tells you where to start. If you want a medical assessment of a food intolerance or allergy, that is a job for your GP.

How long does an elimination diet take?

The core elimination phase is six weeks, and reintroducing foods one at a time afterwards can take several more weeks depending on how many you’re checking. If you’d like longer to explore, that’s fine — just remember the 90-day money-back guarantee asks you to follow your plan for at least 6 weeks with a food diary, so start your diary on day one. You can begin any time after your IntoleranceLab results arrive, and it’s worth doing it alongside your GP or a registered dietitian.

Can I be intolerant to a food I’ve eaten my whole life?

Yes. Intolerances can develop at any age and may change over time. Stress, getting older, and changes in your digestive health can all affect how well your body handles certain foods.

What if I can eat small amounts of a food but not large portions?

That pattern is more typical of an intolerance than an allergy. Intolerances are often dose-dependent — a little may sit fine, while a larger amount brings on symptoms. When you reach the reintroduction stage of your elimination diet, you can experiment carefully with portion sizes and see what your own body prefers.

Why does my GP need to be involved?

Your GP can rule out underlying conditions such as coeliac disease or other digestive disorders, check you’re otherwise well before you start an elimination diet, and refer you to a registered dietitian for guidance. They also make sure nothing more serious is being missed if your symptoms carry on.

Related reading

• Signs of food intolerance
• How hair testing works
• Explore bloating