Allergy Patch Test: What is it? What is it for? Meaning of the Results

by contact. In particular, this specific test that allows the identification of the etiological agents (allergens) responsible for allergic contact dermatitis (ACD).

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The patch test involves the application on the patient's skin of some non-absorbent discs (from 20 to 150 wells), each containing an allergen potentially responsible for the dermatitis (eg nickel, chromium preservatives, dyes, perfumes, etc.). L " allergen is released slowly for 48 hours and, if the person is susceptible to a particular substance, a local inflammatory reaction appears.

, one of irritative origin - independent of the immune system - and one allergic in which the immune cells produce an inflammatory response directed against the substance mistakenly considered dangerous.

For further information: Contact Dermatitis , soaps and detergents, plants (eg poison ivy), components of topical ointments or drugs (antibiotics, anesthetics, antihistamines) are just some of the allergens tested with the patch test.

The following table provides a brief overview of the substances most frequently involved in the development of allergic contact dermatitis:

Causes of allergic contact dermatitis Examples Cosmetics, perfumes and detergents Vaseline (pomades and ointments), parabens (preservatives), paraphenylenediamine free base in hair dyes (dyes) and other compounds present in personal and home hygiene products. Chemical substances used in the textile or footwear industry, in construction and in other industrial products Many substances, such as epoxy resins, natural and synthetic textile fibers, dyes, dressings, additives to rubber, leather and related adhesives, pesticides and formaldehyde in plastics and adhesives. Metallic compounds, chromium, cobalt, mercury and nickel

• Occupational exposure to various materials (eg potassium dichromate commonly used in construction);
• Personal effects and clothing accessories (eg belt buckles, watches and jewelry).

Volatile substances Various compounds present in the environment and transported by air in the form of vapors, gases, fumes, droplets and solid particles (eg glass fibers, perfumes, cement and wood dust). Topical medications

• Antibiotics (eg bacitracin and neomycin);
• Antihistamines (e.g. diphenhydramine);
• Anesthetics (eg benzocaine);
• Antiseptics (e.g. thimerosal and hexachlorophene);
• Stabilizers (e.g. ethylenediamine and derivatives).

Plants and vegetable substances Poison ivy, rosin (derived from pine resin), Peru balsam (sap from a South American plant used in the pharmaceutical and cosmetic industry) and ragweed pollen.

The patch test can help identify the type of contact dermatitis afflicting the patient and assess the body's responses to the various substances used. Generally, irritative forms are common to all people, while allergic forms are less widespread and highly customized.