A food allergy involves an immune-system reaction and can sometimes cause anaphylaxis. A food intolerance usually involves difficulty digesting or processing a food and does not cause a life-threatening allergic reaction.
Although the symptoms can sometimes overlap, allergies and intolerances involve different processes and may require different forms of testing or clinical investigation.
Understanding the difference is important before arranging a test or removing foods from your diet. A blood test designed to investigate an IgE-mediated allergy cannot diagnose lactose intolerance or every possible cause of digestive symptoms.
Nadcell Mindcare Clinic provides private adult allergy testing in Glasgow using specific IgE blood tests. We do not provide food-intolerance testing through this service.
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Food allergy | Food intolerance | |
What is involved? | The immune system reacts to a food or a particular food protein. | The body has difficulty digesting or processing a food or ingredient. |
When can symptoms begin? | IgE-mediated reactions often begin within minutes or up to around two hours. Other forms of food allergy may be delayed. | Symptoms commonly develop several hours after eating. |
Common symptoms | Hives, itching, swelling, coughing, wheezing, vomiting or breathing difficulties. | Bloating, wind, abdominal pain, diarrhoea, nausea or constipation. |
Can it be life-threatening? | Some food allergies can cause anaphylaxis. | Food intolerance does not cause anaphylaxis. |
How may it be investigated? | Clinical history, specific IgE blood tests, skin-prick testing and, in specialist settings, supervised food challenges. | Food and symptom diaries, supervised elimination and reintroduction, and condition-specific investigations such as a lactose breath test. |
Symptoms alone cannot confirm whether you have an allergy or intolerance. Your medical history, the timing of the reaction, the amount consumed and whether you regularly tolerate the food all need to be considered.
A food allergy occurs when the immune system reacts to a food that would normally be harmless.
In an IgE-mediated food allergy, the body produces immunoglobulin E (IgE) antibodies specific to a particular allergen. When the person encounters that allergen again, the immune response can produce symptoms affecting the skin, digestive system, airways or circulation.
Common food allergens include:
It is possible to be allergic to other foods. The type and severity of an allergic reaction can also vary between people and occasions.
Possible food-allergy symptoms include:
Digestive symptoms can occur as part of an allergic reaction, but bloating or abdominal discomfort alone does not automatically indicate an allergy.
A clinician may consider what was eaten, how much was consumed, how quickly symptoms appeared and whether the same food has previously been tolerated.
Some food allergies can cause a severe and potentially life-threatening reaction known as anaphylaxis.
Call 999 immediately if someone develops:
If the person has been prescribed an adrenaline auto-injector, use it according to their emergency treatment plan and then call 999.
Do not wait for an allergy-testing appointment during a suspected medical emergency. The NHS food-allergy guidance provides further information about symptoms, testing and emergency action.
A food intolerance occurs when the body has difficulty digesting or processing a particular food or ingredient.
Unlike an IgE-mediated food allergy, a food intolerance does not normally involve the immune system and cannot cause anaphylaxis.
Symptoms may be influenced by how much of the food is consumed. Some people with an intolerance may be able to tolerate a small amount without experiencing symptoms, although this depends on the individual and the underlying cause.
Lactose intolerance is a common example. It occurs when the body does not produce enough lactase, the enzyme needed to digest lactose, the natural sugar found in milk and many dairy products.
This is different from an allergy to cow’s milk proteins.
Food-intolerance symptoms commonly affect the digestive system and may include:
Some people also report headaches, tiredness or skin symptoms. However, these complaints are not specific to food intolerance and may have many possible causes.
Symptoms frequently develop a few hours after eating and can last for several hours or days.
Recurring symptoms should be discussed with an appropriate healthcare professional, particularly when accompanied by unexplained weight loss, blood in the stool or a persistent change in bowel habits.
“Food sensitivity” is frequently used as a broad description for symptoms that appear to be associated with food.
However, it lacks a consistently applied clinical definition. It may be used informally to describe an intolerance, a non-IgE reaction or another adverse response to food.
A food sensitivity test is therefore not automatically the same as an allergy test.
Nadcell’s blood-testing service measures specific IgE antibodies associated with selected allergens. It does not diagnose a broadly defined food sensitivity or food intolerance.
Anyone considering food sensitivity testing should first understand:
There is no single allergy test that can provide a complete diagnosis without considering the patient’s symptoms and medical history.
Different investigations may be used depending on the suspected reaction.
A specific IgE blood test measures IgE antibodies associated with selected allergens.
This can provide clinically useful evidence that the immune system has become sensitised to a food or another substance. It does not require the patient to be exposed directly to the suspected allergen during the test.
The result must be interpreted alongside:
A positive result indicates sensitisation but does not automatically prove that exposure will cause symptoms or predict the severity of a future reaction.
Skin-prick testing involves placing small amounts of selected allergen solutions onto the skin before gently pricking the surface. Any visible response is normally assessed shortly afterwards.
Skin-prick testing and specific IgE blood testing are different methods of investigating allergic sensitisation.
Nadcell does not provide skin-prick testing. Our Glasgow allergy-testing service uses blood tests.
Patch testing is generally used to investigate delayed skin reactions such as allergic contact dermatitis.
Small amounts of potential contact allergens are applied to the skin using patches. These normally remain in place for approximately 48 hours, with the skin assessed across a series of appointments.
Patch testing is different from specific-IgE food-allergy testing and is not included in Nadcell’s blood-testing service.
A healthcare professional may recommend removing a suspected food for a defined period before carefully reintroducing it and observing whether symptoms return.
This should be planned with appropriate professional support, particularly when removing an important food group.
Do not begin a restrictive diet based solely on an unconfirmed test result.
An oral food challenge involves consuming controlled amounts of a suspected allergen under close medical supervision.
Because it can cause an allergic reaction, the test must only be performed in an appropriate clinical environment where emergency treatment is available.
Do not deliberately expose yourself to a food that may have previously caused a serious reaction.
The most appropriate investigation depends on the suspected intolerance and the symptoms experienced.
The process may include:
There is no single general blood test that can diagnose every form of food intolerance.
Some commercially available tests use IgG antibodies, hair analysis, bioresonance or other methods to claim that they can identify multiple food intolerances. These should be treated cautiously.
The NHS advises that some home food-intolerance tests have limited supporting evidence and may encourage people to avoid multiple foods unnecessarily.
Removing major foods or food groups without appropriate advice can affect nutrition, make eating more difficult and reduce quality of life.
Nadcell provides a range of private blood tests in Glasgow, including three adult allergy blood-testing options.
The comprehensive molecular profile provides broad coverage across more than 300 allergens.
Depending on the profile used, this may include:
This option may be suitable for adults with multiple or difficult-to-identify potential allergic triggers.
The food-only profile investigates specific IgE associated with a selected range of food allergens, including:
This profile investigates allergic sensitisation. It does not diagnose food intolerance.
Individual-specific IgE testing may be appropriate when a particular allergen or a small number of allergens are suspected.
Nadcell’s available individual tests include:
Blood sample collection and result interpretation are included in each displayed price. No GP referral is required.
Nadcell’s allergy-testing service is available only to adults.
An allergy blood test can identify elevated specific IgE associated with a selected allergen.
This may provide evidence that the immune system has become sensitised to that substance and support the investigation of a suspected IgE-mediated allergy.
However, the result is only one part of the assessment and cannot be used independently:
Testing is most useful when the selected allergens are relevant to a credible symptom and exposure history.
If your symptoms and medical history suggest a possible IgE-mediated allergy, Nadcell offers private adult allergy blood testing at its Glasgow clinic.
The team can explain the available profiles, collect your blood sample and provide an interpretation of the laboratory findings.
If allergy testing is unlikely to answer your concern, another form of clinical investigation may be more appropriate.
