Allergy tests — what they can identify
Reviewed by the My London Pharmacy clinical team, Trishla Shah, Pharmacist Independent Prescriber
·29 July 2026
·7 min read
Quick answer
Allergy tests help identify substances your immune system may react to, such as pollen, foods, pets or dust. Common types include blood tests and skin prick tests. Results only make sense alongside your symptoms, so a clinician's interpretation is essential to reach a reliable answer.
What an allergy is and why testing helps
An allergy is a reaction by your immune system to a substance that is usually harmless, known as an allergen. Common triggers include pollen, house dust mites, animal dander, certain foods, insect stings and some medicines. When someone with an allergy encounters their trigger, the immune system overreacts, which can cause symptoms ranging from mild sneezing, itching, watery eyes or a rash through to more significant reactions.
Allergy testing aims to identify which substances your immune system may be reacting to. This can help make sense of ongoing or seasonal symptoms and guide how to manage them, for example by knowing what to try to avoid or by informing a conversation about treatment. Testing is used within the NHS and privately, and its real value comes when results are interpreted alongside your history and symptoms rather than in isolation, since a test result on its own does not always tell the full story.
Common types of allergy test
There are a few main ways to test for allergies, and the most suitable approach depends on your symptoms, your history and sometimes the type of allergen in question:
- Blood tests measure specific antibodies in the blood that are linked to allergic responses to particular allergens. They can be useful when a skin test is not suitable, for example if you have a skin condition or cannot stop antihistamines.
- Skin prick tests involve placing a tiny amount of an allergen on the skin, usually on the forearm, and observing whether a small raised reaction develops over a short time.
- Supervised challenge testing, where a substance is introduced carefully under close medical supervision, is sometimes used for certain allergies in specialist settings.
Each method has its own strengths and situations where it is most appropriate. A clinician can advise which type of testing is likely to be most useful for you, and whether more than one approach would help build a clearer picture.
What allergy tests can identify
Allergy tests can help point towards a wide range of common triggers. These often include airborne allergens such as grass, tree and weed pollens, house dust mites and animal dander, as well as foods and other substances relevant to your symptoms. Identifying a likely trigger can be both reassuring and practical, giving you a clearer idea of what may be contributing to your symptoms and where to focus any changes. More detailed testing, sometimes called component-resolved testing, can occasionally look at reactions to specific proteins within an allergen, which may help build a more precise picture in certain food, venom or pollen allergies. It is worth knowing, though, that a test largely measures sensitisation rather than how severe a future reaction might be, so a result cannot reliably predict the strength of any reaction on its own.
That said, a positive test result shows sensitivity to a substance, which is not always the same as a clinically important allergy. Some people have a positive result to something that does not actually cause them any problems in everyday life. This is exactly why results are read together with your real-world symptoms, so that findings translate into meaningful, practical guidance rather than unnecessary changes. Knowing what a test does and does not prove helps you get genuine value from it.
Allergy versus intolerance
It is helpful to understand the difference between an allergy and an intolerance, as the two are often confused. An allergy involves the immune system and can produce a relatively rapid reaction after contact with the trigger. An intolerance, such as difficulty digesting certain foods, does not involve the same immune response and tends to cause different, often slower symptoms such as bloating or discomfort.
Allergy tests are designed to look at immune-related allergy rather than intolerance, and they are not a reliable way to diagnose food intolerances. Some tests marketed directly to the public for intolerance are not supported by strong evidence and can be misleading, sometimes prompting people to cut out foods unnecessarily. If your symptoms suggest an intolerance rather than an allergy, a clinician can advise on a more appropriate approach, which may involve carefully reviewing your symptoms, keeping a food and symptom diary, or a structured plan of changes.
Understanding your results
Allergy test results only make sense in the context of your symptoms. A result indicating sensitivity to a substance is a piece of the picture, not a diagnosis on its own. Equally, a negative result does not always completely rule out a reaction, and false results in either direction are possible, which is why no single test is treated as the final word.
For these reasons, professional interpretation is essential. A clinician can bring your test results together with your history and the pattern of your symptoms, including when and where they occur, to reach a reliable conclusion and suggest how to manage things going forward. They can also advise whether further assessment or referral to a specialist allergy service would be helpful. Attempting to interpret results alone can lead to unnecessary avoidance of foods or activities, or to missing a genuine trigger, so support with interpretation is a valuable part of the process.
Managing allergies day to day
Once a trigger has been identified and confirmed in the context of your symptoms, the focus shifts to managing it. For many people this involves a combination of reducing exposure where practical and using appropriate treatments to keep symptoms under control. For pollen allergies, for example, this might mean being mindful of high pollen days, while for dust mites it might involve changes at home.
Treatment options vary depending on the type and severity of your allergy, and what suits one person may not suit another. A clinician can talk through suitable ways to manage your symptoms based on your individual circumstances, and explain when it is important to seek further help. Having a clear, personalised plan often makes allergies far easier to live with and reduces their impact on daily life.
Getting tested and next steps
If you are considering allergy testing, a useful starting point is describing your symptoms and when they happen, as this often gives strong clues about likely triggers and guides which tests are worthwhile. Choosing the right test for your situation makes the results far more meaningful and avoids unnecessary checks.
Once results are available, having them explained in the context of your symptoms is the most valuable step, so you understand what they indicate and how best to respond. The My London Pharmacy team can talk through your circumstances, help you understand what your results mean, and support you in deciding how best to manage your symptoms going forward.
Recognising a serious allergic reaction
Most allergic reactions are mild and settle with time or simple treatment, but it helps to know the signs of a serious reaction, known as anaphylaxis. This is uncommon but needs emergency care. Warning signs can include swelling of the lips, tongue, mouth or throat; difficulty breathing or noisy, wheezy breathing; a tight chest; feeling faint, dizzy or lightheaded; a sudden widespread rash; and a strong sense that something is seriously wrong. These symptoms can come on quickly, sometimes within minutes of contact with a trigger, and they can affect more than one part of the body at once.
If you think someone is having a severe allergic reaction, call 999 immediately and say you suspect anaphylaxis. Anyone who has been prescribed an adrenaline auto-injector should use it without delay and then call for help, even if they feel they may be overreacting. People who have had a serious reaction before are usually reviewed by a specialist allergy service, which can help confirm the trigger, provide a written emergency plan and prescribe the medicines to carry day to day. Knowing what to watch for, and having a clear plan, offers real reassurance for anyone living with a significant allergy, and it is something a clinician can talk through with you.
Frequently asked questions
What can allergy tests identify?
They can point towards triggers such as pollen, house dust mites, animal dander, foods and other allergens. Results only make sense when read alongside your symptoms.
What is the difference between a blood test and a skin prick test?
A blood test measures allergy-related antibodies in a sample, while a skin prick test looks for a small reaction on the skin. A clinician can advise which is more suitable for you.
Can allergy tests diagnose food intolerance?
No. Allergy tests look at immune-related allergy, not intolerance, and are not a reliable way to diagnose food intolerances. A clinician can suggest a more appropriate approach for suspected intolerance.
Does a positive result mean I am definitely allergic?
Not always. A positive result shows sensitivity, which is not the same as a clinically important allergy, so it must be interpreted alongside your real-world symptoms.
Why should a clinician interpret my results?
Results can be positive or negative without telling the full story, and false results are possible. A clinician combines your results with your history to reach a reliable conclusion.
What happens once my trigger is identified?
The focus shifts to managing it, often by reducing exposure where practical and using suitable treatments. A clinician can help you put together a personalised plan for your circumstances.