Contact Allergy or Allergic Contact Dermatitis

Adults and children can develop allergic contact dermatitis or skin rashes (eczema) caused by contact with ingredients in personal care products or allergens encountered in nature such as poison ivy. Examples of product allergens included chemical fragrances, nickel found in costume jewelry, and preservatives found in many products applied to the skin. Typically, itchy, red and bumpy rashes begin days after contact with the causative substance, making it very challenging to identify the cause. Our allergists perform allergy patch testing to identify the allergic causative agent and source. Once identified avoidance of products containing allergens usually leads to improvement or resolution of the rash.
Anyone can develop skin irritation (irritant contact dermatitis) with repetitive hand washing, wet work or with exposure to caustic chemicals in household cleaning agents. However, relatively fewer people develop allergic contact dermatitis caused by development of immune hypersensitivity to specific substances.

Patch Testing to Identify Causative Allergens
A closed patch test is performed on the back. Patch tests identify delayed allergic reactions characteristic of allergic contact dermatitis. These are different from skin prick tests that identify immediate allergy to airborne allergens such as pollen. Patch testing is performed by placing panels of test materials on aluminum discs that are taped on the back for 48 hours. After 48 hours, the patches are removed and an initial reading is performed. Patients are asked to return for a final reading 2 days or 5 days later. A positive test will show a red, raised area on the skin at the test site, often with itching. In this way, specific allergens can be confirmed and avoided in the future.

Patch Testing for Metal Allergy
Metal contact allergy is a delayed-type hypersensitivity reaction to metal. The most common offender is nickel; however, sensitization occurs to other metals such as cobalt or chromium. Patch testing to the common metals used in manufacturing prosthetic devices (such as artificial knees or hips) is often done to identify presence of metal allergy prior to placement of a device. At Advanced Allergy, we have a customized patch test panel for evaluating allergy to common sensitizing metals in orthopedic devices and for surgical cement materials.