Food allergy vs intolerance: the quick comparison
Food allergy
An immune reaction to a food. Some reactions can be severe, including anaphylaxis.
Food intolerance
Often digestive or metabolic, with different mechanisms. Does not cause allergic anaphylaxis.
Coeliac disease
An autoimmune response triggered by gluten. Not an allergy and not a simple intolerance.
| Feature | Food allergy | Food intolerance |
|---|---|---|
| Main mechanism | Immune system reaction to a food | Usually difficulty processing or responding to a food component without an allergic immune mechanism |
| Common examples | Peanut, milk, egg, fish or sesame allergy | Lactose intolerance |
| Typical symptoms | May include hives, swelling, vomiting, breathing problems or other reactions | Often digestive symptoms such as bloating, wind, abdominal pain or diarrhoea |
| Can symptoms be serious? | Yes, some allergic reactions can cause anaphylaxis | Symptoms can be significant, but ordinary food intolerance does not cause allergic anaphylaxis |
| Does the amount matter? | Small amounts can trigger reactions in some people | Symptoms are often dose-dependent, although this varies |
| Diagnosis | Medical history and appropriate allergy testing or assessment | Depends on the suspected intolerance and may involve dietary assessment or specific tests |
| Ingredient checking | Avoidance depends on the diagnosed allergen and medical advice | Avoidance or reduction depends on the individual intolerance |
These are general distinctions. Symptoms alone cannot reliably establish a diagnosis.
What is a food allergy?
A food allergy occurs when the immune system reacts to a food or a component of it.
Many familiar food allergies are IgE-mediated. In these reactions, the immune system produces IgE antibodies directed against particular food proteins.
Exposure can trigger the release of chemicals, including histamine, that contribute to allergic symptoms.
However, not all food allergies are IgE-mediated.
Some involve other immune mechanisms and can present differently, particularly in children.
Common food allergies
Examples include allergies to:
- Milk
- Eggs
- Peanuts
- Tree nuts
- Fish
- Crustaceans
- Molluscs
- Sesame
- Soy
- Wheat
People can also be allergic to foods outside these categories.
The UK's 14 regulated allergen categories are a food-labelling framework, not a complete list of everything that can cause an allergy.
What are the symptoms of a food allergy?
Symptoms can vary between people and between reactions.
They may include:
- Itchy skin or hives
- Swelling of the lips, face or tongue
- Tingling or itching in the mouth
- Nausea or vomiting
- Abdominal pain
- Coughing or wheezing
- Breathing difficulties
- Dizziness or faintness
Some reactions involve more than one part of the body.
How quickly do food allergy symptoms appear?
IgE-mediated reactions often begin within minutes to a couple of hours after exposure.
Other immune-mediated food allergies can have more delayed symptoms.
The timing alone does not confirm or rule out an allergy.
Can a food allergy cause anaphylaxis?
Yes.
Anaphylaxis is a potentially life-threatening allergic reaction.
Signs can include breathing difficulty, throat or tongue swelling, circulatory symptoms such as faintness or collapse, and other severe features.
If anaphylaxis is suspected, use prescribed adrenaline immediately according to the person's emergency plan and call 999 in the UK.
Do not wait for a rash to appear. Anaphylaxis can occur without obvious skin symptoms.
Follow emergency service instructions and the person's prescribed treatment plan.
What is a food intolerance?
Food intolerance is a broad term used when someone experiences symptoms after consuming a food without the same mechanism as a food allergy.
Different intolerances have different causes.
For example, lactose intolerance occurs when the body has difficulty digesting lactose because of insufficient lactase enzyme activity.
Other food-related symptoms may involve fermentation of certain carbohydrates, digestive conditions or different mechanisms.
Common intolerance symptoms
These can include:
- Bloating
- Wind
- Abdominal discomfort
- Diarrhoea
- Nausea
Symptoms vary and can overlap with other medical conditions.
Can a food intolerance be serious?
Food intolerances can significantly affect quality of life.
However, ordinary food intolerance does not cause the immune-mediated anaphylaxis associated with certain food allergies.
Severe, persistent or unexplained symptoms still deserve medical assessment.
Milk allergy vs lactose intolerance
This is one of the most important distinctions when reading labels.
Milk allergy and lactose intolerance both involve milk, but the relevant components are different.
Milk allergy
An immune reaction to milk proteins, such as casein and whey. Lactose-free milk still contains them.
Lactose intolerance
Difficulty digesting lactose, the milk sugar. Symptoms are usually digestive, and the amount tolerated varies.
Milk allergy
Milk allergy involves an immune reaction to milk proteins.
These include proteins such as:
- Casein
- Whey proteins
People with milk allergy may need to avoid milk and relevant milk-derived ingredients according to their medical guidance.
Lactose intolerance
Lactose intolerance involves difficulty digesting lactose, the sugar found in milk.
Symptoms are usually digestive.
Some people with lactose intolerance can tolerate small amounts of lactose, while others are more sensitive.
The amount tolerated varies.
Is lactose-free milk suitable for milk allergy?
No, not simply because it is lactose-free.
Lactose-free cow's milk usually still contains milk proteins.
Removing or breaking down lactose does not remove the proteins responsible for milk allergy.
Is whey dairy?
Yes.
Whey is derived from milk and contains milk proteins.
Is lactic acid dairy?
Not inherently.
Despite its name, lactic acid does not necessarily come from milk.
Its source and the particular product matter.
Can someone with milk allergy drink goat's milk?
Goat's and sheep's milk contain proteins that can be similar to those in cow's milk.
They should not be assumed to be suitable alternatives for someone with cow's milk protein allergy.
Read our complete guide to hidden milk ingredient names.
Wheat allergy vs coeliac disease vs gluten sensitivity
These conditions are frequently confused.
All three can lead someone to avoid certain foods, but the reasons differ.
Wheat allergy
Wheat allergy is an immune reaction to wheat proteins.
Symptoms may include skin, digestive or respiratory reactions.
Some wheat allergies can cause anaphylaxis.
A person with wheat allergy may need to avoid wheat even when a food meets a gluten-free standard.
Coeliac disease
Coeliac disease is an autoimmune condition triggered by gluten in genetically susceptible people.
It is not a conventional food allergy or a simple intolerance.
Gluten exposure can cause immune-mediated damage to the lining of the small intestine.
Treatment involves a strict gluten-free diet.
Non-coeliac gluten or wheat sensitivity
Some people experience symptoms associated with gluten-containing or wheat-containing foods without having coeliac disease or wheat allergy.
This is sometimes described as non-coeliac gluten sensitivity or non-coeliac wheat sensitivity.
The mechanisms are not fully understood, and other wheat components may contribute to symptoms in some cases.
It is important to exclude coeliac disease and wheat allergy appropriately before applying this diagnosis.
For a closer look at all three, read our guide to wheat allergy vs coeliac disease vs gluten intolerance.
Comparison
| Condition | Main issue | Important label consideration |
|---|---|---|
| Wheat allergy | Immune reaction to wheat proteins | Wheat and relevant wheat-derived ingredients |
| Coeliac disease | Autoimmune response triggered by gluten | Gluten from wheat, barley, rye and relevant sources |
| Non-coeliac gluten/wheat sensitivity | Symptoms associated with gluten or wheat without coeliac disease or wheat allergy | Individual dietary guidance after appropriate assessment |
Should you stop eating gluten before being tested for coeliac disease?
Not without discussing it with a healthcare professional.
Removing gluten before testing can affect the accuracy of coeliac disease investigations.
Read our wheat and gluten ingredient guide.
Can food allergies develop in adulthood?
Yes.
Some food allergies begin during childhood, while others first appear in adulthood.
The pattern varies by allergen and individual.
A food that someone has eaten previously without difficulty can later become associated with an allergic reaction.
However, a new symptom after eating does not automatically mean an allergy has developed.
Medical assessment is important.
Can you grow out of a food allergy?
Some children outgrow particular food allergies.
Milk and egg allergies, for example, may resolve in some children over time.
Other allergies, such as peanut or certain tree nut allergies, are more likely to persist, although outcomes vary.
Whether an allergy has resolved should be assessed by an appropriate healthcare professional.
Do not test whether an allergy has disappeared by trying the food at home without medical guidance.
Can you develop a food intolerance later in life?
Yes.
For example, lactase activity can decrease with age, contributing to lactose intolerance.
Digestive conditions, infections and other changes may also affect food tolerance.
However, new or persistent digestive symptoms can have several possible causes.
Avoid assuming that a food intolerance is responsible without appropriate assessment.
How are food allergies diagnosed?
Diagnosis depends on the symptoms and suspected mechanism.
A clinician may use:
- Detailed medical history
- Review of the foods involved
- Symptom timing and pattern
- Skin prick testing when appropriate
- Specific IgE blood testing when appropriate
- Supervised oral food challenges in selected circumstances
Can an allergy blood test diagnose an allergy on its own?
Not always.
A positive specific IgE result can indicate sensitisation, which is not necessarily the same as having a clinically significant food allergy.
Test results need to be interpreted alongside the person's history and, where appropriate, other assessments.
Are home food allergy tests reliable?
Many commercially marketed food sensitivity tests lack adequate evidence for diagnosing food allergy or intolerance.
In particular, food-specific IgG tests are not recommended as diagnostic tests for food allergy.
Avoid removing large numbers of foods solely on the basis of an unvalidated test.
How are food intolerances diagnosed?
There is no single test for every food intolerance.
The approach depends on the suspected cause.
For lactose intolerance, assessment may involve a hydrogen breath test or other appropriate clinical approaches.
For other food-related symptoms, a clinician or dietitian may recommend structured dietary assessment.
Should you eliminate foods to see what happens?
Elimination diets can sometimes be useful when appropriately planned.
However, unnecessarily restrictive diets can lead to nutritional problems, particularly in children.
Seek professional guidance when excluding important food groups or investigating persistent symptoms.
Why do food allergies and intolerances sometimes look similar?
Both can involve digestive symptoms.
For example, vomiting or abdominal discomfort can occur in some food allergies as well as in food intolerances.
This overlap is one reason self-diagnosis can be unreliable.
The presence of digestive symptoms does not automatically mean an intolerance.
Likewise, symptoms after eating a food do not automatically establish an allergy.
The wider clinical picture matters.
What does this mean when checking food labels?
The difference between allergy and intolerance changes what information is relevant.
Example 1: Milk allergy
A person with milk allergy may need to check for:
- Milk
- Casein
- Whey
- Milk powder
- Milk proteins
- Other relevant milk-derived ingredients
A lactose-free claim is not sufficient.
Example 2: Lactose intolerance
A person with lactose intolerance is concerned with lactose content and their individual tolerance.
Some milk-derived products contain less lactose than others.
However, ingredient names alone do not always establish the exact lactose quantity.
Example 3: Coeliac disease
A person with coeliac disease needs to check for gluten and understand gluten-free labelling.
Barley malt, rye and wheat ingredients may be relevant.
Example 4: Wheat allergy
A person with wheat allergy needs to consider wheat-derived ingredients, even where gluten has been reduced or removed.
Example 5: Peanut allergy
A person with peanut allergy needs to identify peanuts, groundnuts, arachis and relevant peanut-derived ingredients.
The refining of peanut oil and individual clinical advice may also matter.
The same label can therefore mean different things to different people.
Why 'free from' labels can be confusing
A product may be described as:
- Dairy-free
- Lactose-free
- Gluten-free
- Wheat-free
- Vegan
- Plant-based
These claims are not interchangeable.
| Claim | Main meaning | Important limitation |
|---|---|---|
| Lactose-free | Addresses lactose content | May still contain milk proteins |
| Dairy-free | Indicates absence of dairy ingredients in the context of the claim | Check suitability and cross-contact information |
| Gluten-free | Meets the applicable gluten-free standard | May contain other allergens |
| Wheat-free | Addresses wheat | Does not automatically establish absence of barley or rye gluten |
| Vegan | Intended to exclude animal-derived ingredients | Does not guarantee absence of allergen cross-contact |
| Plant-based | Describes plant-focused ingredients | May contain soy, nuts, sesame or wheat |
Is vegan food suitable for milk allergy?
Not automatically.
A vegan product may contain no deliberately added milk ingredients but carry a milk cross-contact warning.
It may also contain other allergens.
Read our guide to food labels for allergies.
What about 'may contain' warnings?
A statement such as:
May contain peanuts
generally refers to possible unintended allergen presence through cross-contact.
It is different from peanuts being deliberately included as an ingredient.
Does 'may contain' matter for intolerance?
It depends on the individual's requirements and the substance involved.
Allergy and intolerance are different, so the relevance of possible trace exposure can differ.
A person with a diagnosed allergy should follow their allergy-management guidance.
Someone with an intolerance may have different tolerance thresholds, but those should not be assumed from the warning alone.
Can an app decide whether a 'may contain' warning is acceptable?
No.
An app can help identify the warning.
It cannot determine an individual's clinical risk or tolerance.
Read our complete guide to 'may contain' warnings.
Are the UK's 14 allergens only relevant to allergies?
The UK's 14 regulated categories are part of food information law.
They include substances associated with different types of adverse reactions.
For example:
- Milk is relevant to milk allergy.
- Cereals containing gluten are important for coeliac disease as well as certain allergies.
- Sulphites can cause sensitivity reactions through mechanisms that are not always conventional IgE-mediated allergy.
The list is a regulatory framework rather than a classification of every medical condition.
Read our guide to the UK's 14 major food allergens.
Can two people need to avoid the same food for different reasons?
Yes.
Consider two people avoiding milk.
One has a diagnosed milk allergy.
The other has lactose intolerance.
They may both avoid some dairy products, but their requirements can differ substantially.
Or consider two people avoiding wheat.
One has wheat allergy.
The other has coeliac disease.
The ingredients, exemptions and food claims relevant to each person may not be identical.
This is why a personalised ingredient list is more useful than assuming everyone avoiding a food has the same condition.
How ClearaScan helps with different dietary requirements
ClearaScan allows users to create personalised Ingredient Guards.
Instead of assuming that everyone needs the same list, each person can select ingredients relevant to their own requirements.
Different people, different rules
One family member may need to avoid milk proteins.
Another may be checking gluten-containing ingredients.
A third may be avoiding particular cosmetic ingredients.
One captured label, multiple profiles
ClearaScan can check recognised ingredient text against multiple profiles without requiring a separate photograph for every person.
Actual ingredient labels
The app reads photographs of the ingredient information on the product you're holding.
This helps users review the current packaging rather than relying solely on a barcode database record.
Important limitations
ClearaScan does not diagnose allergies or intolerances.
It cannot establish whether a food is suitable for coeliac disease solely from an ingredient list, measure lactose or allergen protein levels, or determine an individual's tolerance threshold.
A result with no flagged matches is not a guarantee of safety.
Always verify the original label and follow relevant medical guidance.
