🌿 Allergies and Intolerances: A Complete Guide for Patients

Reactions to foods, pollen, mould, animals, or chemicals are increasingly common. But many people don’t realise there’s a difference between allergies and intolerances — and that understanding this difference can help protect your health and guide treatment.

This guide explains:

• What allergies and intolerances are

• How they develop

• How they differ

• Why more people are affected than in the past

• What to do if you’re experiencing symptoms

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🤧 What Is an Allergy?

An allergy happens when your immune system overreacts to a harmless substance (called an allergen). Instead of ignoring the substance, your body sees it as a threat and releases histamine and other chemicals, causing inflammation and symptoms.

✅ Common Allergy Symptoms

• Sneezing, runny or blocked nose

• Itchy eyes or throat

• Wheezing or coughing

• Rashes or hives

• Swelling of lips, face, or throat

• Nausea or vomiting

• In severe cases: anaphylaxis, a life-threatening reaction that requires emergency treatment

🧴 Common Allergy Triggers

• Pollen

• Mould spores

• Dust mites

• Pet dander

• Foods (e.g., peanuts, shellfish, eggs)

• Insect stings

• Latex

• Medications (e.g., penicillin)

Onset: Usually within minutes to 2 hours
Severity: Can range from mild to life-threatening

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🍞 What Is an Intolerance?

An intolerance is when your body has difficulty processing or digesting a substance. It does not involve the immune system and is not life-threatening, though it can be very uncomfortable.

✅ Common Intolerance Symptoms

• Bloating

• Abdominal pain

• Gas or diarrhoea

• Nausea

• Headaches or migraines

• Fatigue or “brain fog”

🧂 Common Intolerance Triggers

• Lactose (milk sugar)

• Gluten (in non-coeliac cases)

• Food additives (e.g. sulphites, MSG)

• Caffeine or alcohol

• Certain fruits and vegetables (e.g., those high in FODMAPs)

Onset: Often delayed – hours after eating
Severity: Not dangerous, but can affect quality of life

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🛑 What About Coeliac Disease?

Coeliac disease is different from both allergies and intolerances. It is an autoimmune condition triggered by gluten (in wheat, rye, barley), where the immune system damages the small intestine.

• Can lead to nutrient deficiencies, fatigue, bone loss, and other complications

• Requires strict lifelong gluten-free diet

• Diagnosed by blood tests and intestinal biopsy

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🩺 Allergy vs Intolerance: Side-by-Side Comparison

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⏳ Can They Develop Over Time?

Yes — both allergies and intolerances can develop at any age, even in adulthood.

• Allergies may appear after repeated exposure, a change in environment, infection, or hormone shift.

• Intolerances may emerge gradually and worsen over time, especially after illness or with changes in gut health.

Can They Go Away?

• Some childhood allergies (e.g., to milk or egg) may fade with age.

• Intolerances can sometimes improve if the gut heals or the irritant is removed temporarily.

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🧬 Why Do Some People Get Allergies or Intolerances?

Several factors increase the risk:

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🔬 Why Are These Conditions Becoming More Common?

Over recent decades, both allergies and intolerances have become more widespread — especially in industrialised countries. Here’s why:

1. Hygiene Hypothesis

• Cleaner environments mean fewer early exposures to bacteria and parasites.

• Immune systems may become overreactive, mistaking harmless things like food or pollen for threats.

2. Environmental Changes

• More pollution, chemical exposure, and indoor living.

• Increased use of cleaning products, synthetic fragrances, and pesticides.

3. Modern Diets

• More processed foods, additives, and preservatives

• Less fibre and fermented food = poorer gut microbiome diversity

4. Changes in Early Childhood Exposure

• Less breastfeeding

• More Caesarean births (altering gut flora)

• Delayed introduction of allergens (now reversed in guidelines)

5. Better Awareness and Diagnosis

• People are more likely to report symptoms

• Testing and knowledge have improved, leading to more diagnoses

6. Stress and Modern Lifestyle

• Stress may worsen sensitivity to foods, chemicals, or allergens

• Stress can also influence gut function and immune balance

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🧪 How Are Allergies and Intolerances Diagnosed?

Allergy Testing:

• Skin prick tests

• Blood tests for IgE antibodies

• Oral food challenge (done in hospital if risk of anaphylaxis)

• Referral to an allergy specialist

Intolerance Testing:

• Elimination and reintroduction diets

• Hydrogen breath tests (e.g., for lactose or fructose)

• Intolerances often require trial and error

Never self-diagnose based on internet lists — mislabeling a symptom could lead to unnecessary food avoidance or missed health risks.

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💊 How Are They Treated?

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🩺 When to See a Doctor

You should speak to your GP if:

• You experience repeated symptoms after certain foods or environmental exposures

• You’ve had severe reactions like swelling, wheezing, or fainting

• You’re unsure whether your reaction is allergy or intolerance

• You’re planning to reintroduce foods or need support with diet changes

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🧭 Final Summary

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Understanding the difference between allergies and intolerances can help you:

• Stay safe

• Manage your symptoms

• Avoid unnecessary restrictions

• Get the care and advice you need

You are not alone — and support is available.

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