Patch Test: What to Avoid Before Undergoing the Examination

The Patch Test (or epicutaneous test) is a fundamental dermatological examination to diagnose the contact allergies, i.e. those skin reactions that occur after exposure to substances such as metals, perfumes, preservatives or chemicals. It is a valuable tool used by dermatologists to identify the causes of chronic or relapsing dermatitis and propose a targeted therapy.

For the results to be reliable, however, it is essential to prepare correctly. Certain behaviours or substances can in fact alter skin reactivity, distorting the results of the examination.

In this guide we will look in detail at what to avoid before the Patch Test and why these precautions are so important.

What is the Patch Test and what is it for?

The Patch Test is an examination non-invasive which consists of applying small patches containing various potentially allergenic substances to the skin (usually on the back). The patches remain in place for 48 hoursafter which they are removed. Next, the dermatologist observes the skin to check for allergic reactions, such as:

• reddening

• itching

• swelling

• appearance of blisters or vesicles

This test is particularly useful for identifying substances responsible for allergic contact dermatitis, such as:

• metals (e.g. nickel)

• cosmetics and perfumes

• chemical preservatives

• hair colours

• industrial products or detergents

What to Avoid Before the Patch Test

1. Antihistamines

The antihistamines are medicines that reduce the symptoms of allergies, such as itching and redness. However, they can reduce skin reactivity and falsify the results of the Patch Test.

• Avoid taking antihistamines for at least 48 hours before the test (unless the doctor indicates otherwise).

• Some common examples: Cetirizine (Zirtec), Loratadine (Claritin), Fexofenadine (Allegra).

If you take these drugs regularly, always inform your dermatologist before the examination.

2. Corticosteroids

I corticosteroids, both topicals (creams or ointments) that systemic (taken by mouth), reduce skin inflammation. For this reason they may masking possible allergic reactions during the Patch Test.

• In the case of cortisone-based therapies for dermatitis, psoriasis or other conditions, your doctor will tell you whether and when to suspend treatment before the test.

3. Solar Exposure

Skin that is tanned or irritated by the sun is not in the ideal condition for the Patch Test. Sun exposure can indeed:

• make the skin more sensitive

• cause false reactions (positive or negative)

• prevent a correct reading of the results

It is advisable avoid direct sunlight for at least a week before the test. In case of recent burns, always notify your dermatologist.

4. Creams, Lotions and Cosmetics

Before the test, it is important not to apply moisturising creams, oils, perfumes or lotions on the back or on the area where the patches will be placed.

• These products create a barrier on the skin which may hinder contact between allergen and skin.

• It is recommended to discontinue the use of cosmetics and similar products at least 24 hours before of the test.

5. Hot Baths and Sauna

The use of hot baths, saunas or steam baths can make the skin more sensitive and increase the risk of irritation. This may distort the results of the Patch Test, as the skin may react more easily to allergens due to increased circulation and surface irritation. To avoid complications, try to avoid these activities in the days leading up to the test.

6. Intense Physical Activity

Strenuous physical activity before and during the Patch Test is not recommended. Sweat may cause the patches to peel off or irritate the skin, affecting the accuracy of the test. It is important to keep the patches dry and in place for the duration of the test, so avoid heavy workouts that could affect the stability of the patches.

What to Do During the Patch Test

While the patches are being applied, there are some important rules to follow to ensure that the test gives accurate results:

• Do not get the area wetAvoid showering or bathing during the two days the patches are on your skin. Water could make the patches peel off or affect the results.
• Do not scratch the skinIf you experience itching under the patches, try to resist the temptation to scratch. Scratching could further irritate the skin and compromise the test results.
• Avoid rubbingWear loose clothing that does not exert pressure or friction on the patches to prevent them from shifting.

If you notice excessive irritation or unbearable discomfort during the Patch Test, contact your dermatologist immediately for further instructions.

What to Expect After the Patch Test

Once the patches are removed, the dermatologist will examine the skin for signs of an allergic reaction. A further check may be necessary after 48-72 hours, as some allergic reactions may be delayed.

The allergic reactions identified by the Patch Test can vary from mild irritation to actual erythema or swelling. If the test is positive, the doctor can advise on how to avoid specific allergens and propose a customised treatment plan.

For more information on treatments for contact allergies, visit our skin allergies page.

FAQ - Frequently Asked Questions about Patch Testing

1. Can I take medication during the Patch Test?

During the Patch Test, it is best to avoid taking drugs that could interfere with the results, such as antihistamines and corticosteroids. However, if you take essential drugs for other medical conditions, inform your dermatologist, who can give you specific instructions.

2. What happens if the patches come off?

If one or more patches come off before the set time, it is important not to reapply them yourself. Instead, contact your dermatologist immediately to find out how to proceed. Loss of a patch could compromise the accuracy of the test, possibly requiring it to be repeated.

3. How long does the Patch Test last?

The Patch Test lasts an average of 48 hours, during which the patches remain applied to the skin. After the patches have been removed, the doctor may ask you to come back for a check-up within 72 hours to assess any delayed reactions.

4. Is the Patch Test painful?

The Patch Test is not painful, but you may experience a slight itching or discomfort if you have an allergic reaction to one of the applied allergens. This discomfort is temporary and generally resolves after the patches are removed.

5. What should I do if it turns out to be an allergic reaction?

If the test is positive for one or more substances, your doctor will give you instructions on how to avoid these allergens in your daily life. You may need to change your cosmetic routine, avoid certain foods or clothing, or change your skin care products.

Conclusions

Properly prepare for the Patch Test is crucial for reliable and accurate results. Avoiding certain medications, topical treatments and behaviours is crucial to ensure that the test can correctly identify the allergens responsible for your skin reactions. By following the directions provided by your dermatologist and the precautions listed in this article, you can ensure that the test is as effective as possible.

For more information on how to manage skin allergies, see our treatment guide for contact dermatitis. To learn more about dermatology and skin care, you can also read this article in Healthline.

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