Allergy patch testing is a diagnostic procedure used to identify substances that cause allergic contact dermatitis. Unlike prick or scratch tests that evaluate immediate allergic reactions, patch testing is designed to identify delayed allergic reactions (type IV hypersensitivity).
The procedure involves applying small amounts of suspected allergens to patches, which are then adhered to the skin, typically on the back. These patches remain in place for 48 hours, after which the skin is evaluated for any reaction. A follow-up evaluation is typically conducted 72-96 hours after application to detect any delayed responses. This systematic approach helps pinpoint specific allergens responsible for skin irritation and inflammation.
Patch testing is primarily used to diagnose allergic contact dermatitis but can also assist in identifying triggers for other skin conditions. Common conditions evaluated through patch testing include:
- Allergic Contact Dermatitis: Caused by allergens such as nickel, fragrances, preservatives, or cosmetics.
- Irritant Contact Dermatitis: To rule out allergic causes and identify irritants.
- Eczema (Atopic Dermatitis): To determine whether allergens contribute to flare-ups.
- Drug-Related Dermatitis: Identifies contact allergies to topical medications like antibiotics or steroids.
- Occupational Dermatitis: Helps pinpoint allergens or irritants related to workplace exposures like equipment, uniforms.
Benefits:
- Accurate Diagnosis: Helps identify specific allergens responsible for allergic contact dermatitis (includes the option to test personal products).
- Personalised Treatment: Enables the creation of a tailored management plan, including avoidance strategies.
- Non-Invasive: A painless procedure that does not involve needles or invasive testing.
- Improved Quality of Life: Identifying and avoiding allergens can significantly reduce symptoms and improve daily living.
Potential Side Effects/Risks:
- Mild Skin Irritation: Redness, itching, or minor swelling may occur at test sites.
- Temporary Discomfort: Patches can feel uncomfortable during the 48-hour application period.
- Allergic Reaction: Rarely, a strong reaction can lead to blistering or prolonged irritation.
- Limitations: Patch testing may not identify all allergens, particularly those causing immediate reactions or irritant contact dermatitis.
Patients undergoing patch testing should follow their dermatologist’s instructions carefully, including avoiding activities that could displace the patches, such as vigorous exercise or excessive sweating. Proper post-test care is essential to ensure accurate results and minimise potential side effects. Organise a referral from your GP to streamline a consultation with our dermatology team today.
