Patch Test

What is a Patch Test?

Patch testing involves a series of tests used to diagnose allergic contact dermatitis. Small quantities of various substances are applied to the skin, and the skin's reaction to these substances is observed over 2 to 3 days. The testing system can include a comprehensive panel of approximately 70-80 allergens or a more focused panel of around 35 allergens.

Skin allergies can lead to significant reactions within the body, manifesting through symptoms such as:

• Itching
• Skin reddening
• Formation of red rashes
• Swelling in the affected area
• Development of scabs due to scar tissue
• Flaking or peeling of the skin

Studies have shown that mothers who smoke during pregnancy are more likely to expose their children to allergies later in life. Additionally, exposure to secondhand smoke increases the risk of developing allergies in both children and infants.

Why is a Patch Test Done?

A patch test is conducted to identify potential allergens that may be responsible for causing eczema, skin irritation, and rashes in patients. This test is commonly used to diagnose the following conditions:

• Hay fever (allergic rhinitis)
• Allergic asthma
• Dermatitis (eczema)
• Food allergies
• Penicillin allergy
• Bee venom allergy

Procedure of The Patch Test

During a patch test, small strips containing allergens are applied to the skin. After 48 hours, the doctor examines the skin for any reactions to these specific allergens. Additionally, between 72 to 96 hours later, the skin is re-evaluated for any adverse reactions. An aggressive response with swollen red rashes suggests an allergy to the substance. Conversely, if the skin shows no signs of reaction, it indicates a lack of allergy to that substance.

Preparation For The Patch Test

It is recommended to wear loose-fitting clothing and ensure that the area to be tested, typically the upper back, is clean and free from impurities.

Inform your doctor if you have a history of severe allergic reactions, are taking medications that may affect the test results, or have specific skin conditions such as psoriasis or eczema.

Precautions For Patch Testing

Follow these precautions while the patches are on your skin to ensure accurate results:

• Keep the patches in their designated places and avoid disturbing them.
• Shield the patch-covered area during showers or baths to prevent water contact, which could affect the test's accuracy.
• Attend both appointments scheduled by your dermatologist as the patches may react differently with time, ensuring comprehensive evaluation.
• Protect the skin with patches from direct sun exposure by wearing clothing that covers the area and seeking shade during intense sunlight, especially in the mid-afternoon.
• Avoid using ointments containing hydrocortisone on the patch area, as this may impact the accuracy of the test results.

Possible Side Effects From Patch Testing

The patches might cause skin irritation, which typically resolves within a few days. Individuals with darker skin may notice temporary changes in skin color, either lighter or darker, which usually self-corrects.

In some cases, patch testing may trigger a flare-up in individuals with psoriasis. Serious side effects from patch testing are rare. However, there's a slight risk of infection or a long-lasting allergic reaction, though this occurs very rarely. Allergic reactions are usually evident within 30 minutes of beginning the test.

Precautions For Patch Testing