Skin allergy testing (Patch testing and skin prick testing)
Tests carried out by a dermatologist or allergy team to find out whether your skin reacts to specific substances, helping to explain a rash or allergy and guide what to avoid.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- There are two main tests: patch testing for delayed (contact) reactions and skin prick testing for immediate reactions.
- Results must be read in light of your history: a positive test does not always cause your symptoms, and a negative test does not always rule an allergy out.
- Patch testing takes several short visits across about a week and you must keep your back dry; skin prick testing is read in about 20 minutes.
- Choose a clinician or allergy service that explains which test you need and what you should do with the result.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Can identify substances your skin reacts to, helping explain a rash or allergy
You expect a single test to identify the exact cause of every rash without considering your history.
Any bumps usually fade within an hour or two. You can return to normal activities, and the results are discussed at the visit.
Clear, written advice on which substances to avoid and where they are found.
Any bumps usually fade within an hour or two. You can return to normal activities, and the results are discussed...
You keep the patches on and your back dry, avoiding sweating, swimming and bathing the area. Some itch under the...
The patches are removed and the skin is examined. Marks from the patches and early reactions may be visible.
The skin is read again, as contact reactions develop slowly. The clinician explains which reactions are relevant...
What is skin allergy testing?
Skin allergy testing looks at how your skin reacts to particular substances, to help explain a rash or suspected allergy and to work out what you may need to avoid. There are two main, quite different tests.
Patch testing is used for delayed reactions, where skin becomes red, itchy or eczema-like a day or two after contact with something such as a metal, fragrance, preservative or rubber chemical. Small amounts of many substances are taped to your back and read over several days.
Skin prick testing is used for immediate reactions, where symptoms come on within minutes, such as hives, sneezing or itchy eyes after contact with things like pollens, animals, dust mites or certain foods. Tiny drops are pricked into the skin of the forearm and read after about twenty minutes.
These tests can show what your skin reacts to, but a positive result does not always explain your symptoms, and a negative result does not always rule an allergy out. They are most useful when interpreted alongside your history by the clinician.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Patch test vs skin prick test
| Feature | Patch test | Skin prick test |
|---|---|---|
| Type of allergy | Delayed (contact) | Immediate |
| Typical triggers | Metals, fragrances, preservatives, rubber | Pollens, animals, dust mites, some foods |
| Where applied | Back | Forearm |
| When read | Over several days, multiple visits | About 20 minutes, one visit |
The two tests answer different questions. Your clinician chooses based on whether your reactions are delayed or immediate, and sometimes both are relevant.
Preparing for your test
- Describe your symptoms clearly: what happens, how soon after contact, and where on the body.
- List substances, products, jobs or hobbies you think might be involved, and bring your own products if asked.
- Tell the team about all your medicines: antihistamines can affect skin prick tests, and steroids or immune-suppressing medicines can affect patch tests.
- Avoid sunbeds and strong sun on the test area beforehand, and do not apply creams to the back before patch testing.
- For patch testing, plan for several visits over about a week and arrange to keep your back dry, avoiding heavy exercise, swimming and getting the patches wet.
- Wear old, loose clothing, as marker pen and tape are used on the skin.
- Mention if you are pregnant or breastfeeding, or if you have widespread active eczema, as testing may need to be timed differently.
What happens
For skin prick testing, the clinician marks small spots on your forearm, places a drop of each allergen, and gently pricks the skin through each drop. After about twenty minutes they measure any raised, itchy bumps and compare them with control drops. It is usually only mildly uncomfortable.
For patch testing, small chambers holding measured amounts of many substances are taped to your back and marked. You go home keeping the area dry. The patches are removed, usually after two days, and your skin is examined, then read again a couple of days later because contact reactions develop slowly. Sometimes a further later reading is needed.
In both cases the clinician interprets the results alongside your history, explains which reactions are likely to matter, and advises what to do next, such as which substances to avoid.
Is this test right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- You expect a single test to identify the exact cause of every rash without considering your history.
- Your skin in the test area is currently very inflamed or sunburnt, which can make results unreliable.
- You cannot stop interfering medicines, such as antihistamines before skin prick testing, when this is needed.
- Your problem points to a different mechanism, such as a non-allergic skin condition, where allergy testing is the wrong test.
- You cannot attend the several visits or keep the area dry as patch testing requires.
Delay or rearrange if…
- You have widespread active eczema or sunburn on the test area that should settle first.
- You are taking medicines that would affect the result and can safely pause them later.
- You are pregnant or breastfeeding and testing can reasonably wait.
- You have a current skin infection at the test site.
- You cannot commit to the patch-testing visits or keeping your back dry right now.
Alternatives to discuss
- A careful history and trial avoidance of a suspected product.
- Blood allergy tests for immediate allergies, where skin testing is not suitable.
- Treating the skin condition first and reviewing whether testing is still needed.
- Specialist allergy clinic referral for complex or severe allergy.
- No testing if avoidance is already clear and effective.
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Benefits
- Can identify substances your skin reacts to, helping explain a rash or allergy
- Guides practical avoidance, which can greatly improve or clear contact dermatitis
- Helps confirm or rule out suspected triggers rather than guessing
- Can support workplace or product changes where a cause is found
- Skin prick testing gives quick results in a single visit
- Provides information to plan management with your clinician
Risks & complications
- Itching, redness or small bumps at test sites that settle over hours to days
- Needing several visits and keeping the back dry for patch testing
- A flare of itching where a true allergy is found
- Results that do not fully explain your symptoms
- A strong local reaction, with blistering or marked itch, at a positive patch site
- Temporary darkening or paling of the skin where a strong reaction occurred
- A new sensitisation to a tested substance (rare with standard testing)
- False positive or false negative results that can mislead if taken alone
- A widespread or severe allergic reaction, which is very rare with skin prick testing and managed in a setting prepared for it
- Persistent skin colour change or, very rarely, a small scar at a strong reaction site
- Infection at a test site
The most important thing to understand is interpretation: tests show what your skin reacts to, not always what is causing your problem. A relevant trigger must fit your history. Skin prick testing for severe allergy is done where staff and equipment can manage a serious reaction. Ask how your results will be explained and what to avoid.
Published figures to discuss
Skin allergy testing is generally safe, and most reactions are limited to the test sites. The key uncertainties are interpretive rather than physical: tests can be falsely positive or falsely negative, and a positive result is only meaningful if it fits your symptoms. Severe whole-body reactions are very rare and mainly a consideration for skin prick or specialist testing, which is done where such a reaction can be managed. Because relevance and accuracy depend so much on the individual and the substance, we describe these in words rather than quoting precise rates.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Local wheal, redness or itching | Common and expected for skin prick tests when a relevant allergen is positive | The reaction is usually short-lived. Antihistamines and some skin conditions can affect test quality. | Guide sourcesClinical context |
| Systemic reaction or anaphylaxis from skin prick testing | Very rare; one paediatric food-allergen series reported systemic reactions in 0.16% and anaphylaxis in 0.05% of patients | Higher-risk testing should be done in an appropriate clinical setting with resuscitation medicines and trained staff available. | Systemic reactions to skin prick testing with food allergens — PMCpmc.ncbi.nlm.nih.govPublished figure |
| False-positive sensitisation | Common interpretive issue | A positive test shows sensitisation, not necessarily a clinically important allergy. It must match the history. | Guide sourcesClinical context |
| False-negative result | Recognised | Antihistamines, poor extracts, very recent reactions, non-IgE disease or a poor skin response can all make a test misleading. | Guide sourcesClinical context |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
There is no physical recovery from these tests. "Afterwards" is mostly about reading the results over the right time and understanding what they mean for what you should avoid.
- Mild itching or redness at test sites for a short time
- Visible marks from the patches and tape on the back for a day or two
- Itching at any positive site that can persist for a few days
- No change at sites where there was no reaction
Aftercare
- Keep your back dry and the patches in place during patch testing as instructed.
- Avoid scratching test sites to reduce irritation and the small risk of infection.
- Use any soothing treatment the clinician recommends for itchy positive sites.
- Make a note of confirmed triggers and learn the names they hide behind on labels.
- Avoid the substances your clinician says are relevant, and ask for an information sheet if available.
- Keep treating your underlying skin condition as advised.
- Arrange any follow-up to review whether avoidance is helping.
- A clear description of your symptoms and their timing
- A list of suspected products, and the products themselves if asked
- A note of medicines, especially antihistamines and steroids
- A plan to keep your back dry for patch testing visits
- Old, loose clothing for the appointments
- A way to receive and discuss your results
- A plan for how to avoid any confirmed triggers
Scars and how they heal
These tests do not normally cause scars. Skin prick testing leaves tiny marks that fade quickly. Patch testing can leave temporary redness, and a strong positive reaction may cause itching, occasional blistering, or a temporary change in skin colour that usually settles. Lasting marks are uncommon.
⚠ Get urgent help if…
- Difficulty breathing, wheeze, swelling of the lips, tongue or throat, or feeling faint after testing (seek emergency help)
- A rapidly spreading rash or widespread hives after a test
- A severe blistering or very painful reaction at a test site
- Spreading redness, heat, swelling or pus at a test site (possible infection)
- A reaction that is getting worse rather than settling after a few days
- Any reaction you are worried about, with no clear advice on who to contact
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your specialist gives you.
Results & realistic expectations
A useful result identifies one or more substances your skin reacts to and, importantly, links them to your symptoms so you know what to avoid. For contact dermatitis, avoiding a confirmed allergen can lead to real improvement or even clearance over time.
Results are not absolute. A positive test shows sensitisation, but the substance may not be causing your current problem, and tests can miss a relevant trigger or react to something that is not relevant. This is why the clinician interprets them with your history rather than from the test alone.
A confirmed contact allergy is usually lifelong, so avoidance generally needs to continue indefinitely. Immediate allergies can change over time, and some, particularly certain childhood food allergies, may lessen, so results may need reviewing. New sensitivities can also develop, so testing may be repeated if your pattern of symptoms changes.
Related tests, treatments or support
Skin testing is often combined with a detailed history and, where relevant, blood allergy tests for immediate allergies. Patch and prick testing are sometimes both used when it is unclear whether reactions are delayed or immediate. Results usually feed into a wider plan for managing eczema, dermatitis or allergy.
Follow-up & long-term care
Skin prick results are discussed at the visit. Patch test results are explained at the final reading, with written advice on relevant allergens where possible. You may be offered follow-up to check whether avoidance is helping and to review any treatment for your skin or allergy.
- Keep avoiding confirmed triggers and check product labels for the names they appear under.
- Carry an allergen information sheet or list if one is provided.
- Review results if your symptoms change or new reactions appear.
- Continue any agreed treatment for your underlying skin or allergic condition.
Repeat, follow-on and what comes next
- Testing is sometimes repeated or extended if results do not explain your symptoms.
- A negative result may be followed by trial avoidance or further testing.
- Results may be reviewed over time, as allergies can change and new ones develop.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- Clear, written advice on which substances to avoid and where they are found.
- An honest explanation of what positive and negative results do and do not mean.
- A plan to manage itchy or strong reactions at test sites.
- Follow-up to check whether avoidance is improving your symptoms.
- A clear emergency plan if a severe reaction ever occurs.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- Which test is needed (skin prick, patch, or both)
- How many allergens or extra patch series are tested
- Whether your own products are tested
- The number of visits required, especially for patch testing
- The seniority and experience of the clinician or service
- Whether follow-up to discuss results and avoidance is included
- Any letters or reports requested
- The clinician's or service's fee and which test it covers
- The number of visits included for patch testing
- Whether extra allergen series or your own products cost more
- Whether a follow-up to explain results and advise on avoidance is included
- What happens if results are negative or inconclusive
- Any charge for written allergen advice, letters or further testing
- The cancellation policy and who to contact with concerns
On the NHS? Skin allergy testing is available on the NHS when clinically needed, usually after referral; private testing is mainly used for speed or convenience.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Treating any positive result as the cause without checking it fits your history.
- Not explaining that a negative result does not fully rule an allergy out.
- No clear advice on what to avoid and the names a trigger hides behind.
- Not warning that positive sites can itch or blister for several days.
- No plan for managing a strong or severe reaction during testing.
Marketing red flags
- "Complete allergy profile" claims from a single broad test.
- Unvalidated tests, such as some hair, IgG food intolerance or bioresonance tests, sold as allergy testing.
- Promising to identify the cause of every rash.
- Long, expensive allergen panels with no link to your actual symptoms.
- Testing offered without anyone interpreting it against your history.
Choosing a specialist safely
- Check the specialist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good specialist will welcome every one of these.
- Which test do I need, and why is it the right one for my symptoms?
- How will you decide whether a positive result is actually causing my problem?
- What should I do if the test is negative but my symptoms continue?
- Which medicines should I stop before testing, and for how long?
- If you find a trigger, how will you help me avoid it day to day?
- What is the plan if I have a strong reaction during or after testing?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the specialist who carries out my test, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this test not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
Can I have skin allergy testing on the NHS?
What is the difference between a patch test and a skin prick test?
Does it hurt?
Can the test tell me exactly what is causing my rash?
Do I need to stop my medicines first?
Why does patch testing take a whole week?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: NHS — Contact dermatitis: diagnosis British Association of Dermatologists — Contact dermatitis British Society for Allergy & Clinical Immunology (BSACI) — patient information NHS — Allergy testing (skin prick and other tests) Systemic reactions to skin prick testing with food allergens — PMC ASCIA — Skin prick testing manual
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
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