If you have ever felt unwell after eating a particular food, you are not alone. According to the NHS, food allergies affect around 2% of UK adults, while food intolerances are thought to be far more common — potentially affecting up to 20% of the population. But the terms "sensitivity," "intolerance," and "allergy" are often used interchangeably, which creates real confusion. Understanding the difference is not just a matter of semantics — it affects how you manage your symptoms and when you need medical help.
While the boundaries between these terms can blur in everyday conversation, medical professionals in the UK generally distinguish between three types of adverse food reactions. Each involves different mechanisms in the body and carries different levels of risk.
A food allergy is the most serious of the three. It occurs when the immune system mistakenly identifies a food protein as a threat and produces Immunoglobulin E (IgE) antibodies to fight it. This triggers an allergic reaction that can range from mild (hives, itching) to severe and life-threatening (anaphylaxis).
A food intolerance does not involve the immune system. Instead, it occurs when the body has difficulty digesting a particular food or food component. The most well-known example is lactose intolerance, where the body lacks sufficient lactase enzyme to break down the sugar in milk.
"Food sensitivity" is not a precise medical term in the way allergy and intolerance are. It is often used as an umbrella term to describe any adverse reaction to food. Some healthcare professionals use it specifically for non-IgE-mediated immune responses — reactions that involve the immune system but not IgE antibodies. These sit somewhere between classical allergies and intolerances.
One of the most helpful ways to distinguish between the three conditions is by comparing their typical symptoms. The table below outlines the most common symptoms associated with each type of reaction.
| Symptom | Food Allergy | Food Intolerance | Food Sensitivity |
|---|---|---|---|
| Hives / skin rash | Common (rapid) | Rare | Sometimes (delayed) |
| Swelling (lips, tongue, throat) | Common (serious) | No | No |
| Difficulty breathing | Yes (anaphylaxis) | No | No |
| Bloating | Sometimes | Very common | Common |
| Stomach cramps | Sometimes | Very common | Common |
| Diarrhoea | Sometimes | Common | Sometimes |
| Nausea / vomiting | Common | Sometimes | Sometimes |
| Headaches / migraines | Rare | Sometimes | Common |
| Fatigue | Rare | Sometimes | Common |
| Joint pain | Rare | Rare | Sometimes |
| Eczema flare-up | Sometimes | Rare | Sometimes |
| Onset timing | Minutes to 2 hours | Hours to 1 day | Hours to days |
Source: NHS Choices; British Society for Allergy & Clinical Immunology (BSACI); Allergy UK
Getting the right diagnosis is important because treatment and management differ significantly between the three conditions. Here is what the NHS and UK allergy specialists recommend for each.
Food allergies should always be diagnosed by a qualified medical professional. The NHS and BSACI recommend the following approaches:
There is no single definitive test for most food intolerances. The NHS recommends:
Because food sensitivity is a less precisely defined category, diagnosis typically relies on:
The NHS, BSACI, and Allergy UK explicitly advise against commercial IgG blood tests, hair analysis, vega testing, and kinesiology for diagnosing food reactions. These tests lack scientific evidence and can lead to unnecessary dietary restrictions. Always seek NHS-approved diagnostic methods.
Understanding the severity spectrum is crucial. Here is a straightforward guide to when each type of food reaction becomes a medical concern.
Any confirmed food allergy should be managed with a clear avoidance plan and, where appropriate, an emergency action plan. The Food Standards Agency (FSA) requires UK food businesses to declare the 14 major allergens on food labels and menus. If you carry an adrenaline auto-injector (EpiPen), make sure it is always in date and accessible.
Call 999 immediately if someone experiences difficulty breathing, swelling of the tongue or throat, dizziness, confusion, or collapse after eating. Use the adrenaline auto-injector if available.
Food intolerances are not life-threatening, but they can significantly affect quality of life. Persistent symptoms — especially unexplained weight loss, blood in stools, or severe abdominal pain — should always be investigated by your GP to rule out other conditions such as coeliac disease, inflammatory bowel disease, or bowel cancer.
If you notice recurring symptoms that you cannot explain — fatigue, brain fog, joint aches, skin issues — after eating certain foods, it is worth tracking these patterns and discussing them with your GP or a registered dietitian. While not immediately dangerous, chronic food sensitivities can affect your wellbeing over time.
Regardless of whether you suspect an allergy, intolerance, or sensitivity, keeping a detailed food and symptom diary is one of the most powerful first steps. The NHS recommends this as a starting point for investigating adverse food reactions.
An effective food diary should include:
After 2-4 weeks of consistent tracking, patterns often become clear. You might discover that your bloating always follows meals containing a specific ingredient, or that your migraines correlate with certain foods consumed the day before.
NutraSafe makes this process straightforward by allowing you to log meals, scan food ingredients, and track symptoms in one place — helping you and your healthcare provider identify patterns that might otherwise be missed.
If you suspect a food allergy, do not attempt to diagnose it yourself. See your GP, who can refer you to an NHS allergy clinic. For suspected intolerances, your GP may refer you to a registered dietitian for a supervised elimination diet. Avoid self-restricting your diet without professional guidance, as this can lead to nutritional deficiencies.
NutraSafe helps you log meals, scan ingredients, and record symptoms — making it easier to identify whether you are dealing with a sensitivity, intolerance, or something that needs medical investigation.
Download Free on the App StoreA food allergy involves the immune system producing IgE antibodies in response to a food protein, causing rapid and potentially life-threatening reactions such as anaphylaxis, swelling, and hives. A food intolerance does not involve the immune system — it is typically a digestive issue where the body struggles to break down certain foods, causing symptoms like bloating, cramps, and diarrhoea. Allergies can be fatal; intolerances are uncomfortable but not dangerous.
The terms are often used interchangeably, but they are not identical. "Food sensitivity" is a broad umbrella term that can include both immune and non-immune reactions. Some healthcare professionals use it to describe non-IgE-mediated immune responses, which sit between classical allergies and intolerances. In everyday UK usage, food sensitivity and food intolerance are typically treated as the same thing.
Food allergies are diagnosed through NHS-approved methods including skin prick tests, specific IgE blood tests, and supervised oral food challenges conducted by allergy specialists. The NHS does not recommend commercial IgG blood tests, hair analysis, or kinesiology testing, as these lack scientific evidence. Your GP can refer you to an NHS allergy clinic if needed.
Yes. Food intolerances can develop at any age. Lactose intolerance, for example, often develops in adulthood as the body produces less lactase enzyme over time. Stress, illness, gut infections, and changes in gut bacteria can all trigger new intolerances. This is why keeping a food diary is helpful — it can reveal new patterns as your body changes.
See your GP urgently if you experience swelling of the lips, tongue, or throat, difficulty breathing, rapid heartbeat, dizziness, or widespread hives — these suggest an allergic reaction. Call 999 if symptoms are severe. For non-urgent symptoms like persistent bloating, diarrhoea, or skin issues after eating certain foods, book a standard GP appointment. They can arrange testing or refer you to a dietitian.
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Last updated: February 2026