Allergic Contact Dermatitis: Deriving the most benefit from patch testing

September 1, 2007

The human body can theoretically be allergic to any substance in nature, and the usual allergenic suspects have essentially remained the same. If patch testing is correctly done, the physician is able to uncover the antigen or antigens that cause a patient's dermatitis.

Key Points

Hershey, Pa. - Patch testing provides an opportunity to cure the patient of a given allergy, according to one specialist.

Some have said that the greatest abuse of patch testing is a failure to use the test. In order to make standard allergens work, they have to be used frequently.

"Though patch testing is a very practical way and, in some cases, instrumental in exposing an allergy that a patient may have, many dermatologists do not use it. The reasons for this may be that they believe that the history is sufficient in making a clear diagnosis, it is just too time consuming, or because of poor reimbursement," says Bryan E. Anderson, M.D., assistant professor of dermatology, Penn State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pa.

Patch testing particulars

He says patch testing does not have to be a drawn-out procedure.

Physicians can choose to use a T.R.U.E. test. This prefilled system of 23 antigens is fast and easy to administer. He adds that the FINN Chamber system is a bit more complicated and more time-intensive but is more flexible. Both methods use standardized antigen concentrations to avoid false positives and negatives. Irritation is the number one cause of false positives.

"You may not want to patch test every patient. Those who should be patch tested are anyone with a chronic dermatitis, especially of the hands and feet; patients with a highly suggestive history or distribution; a dermatitis that does not respond to therapy; as well as occupationally related dermatitis," Dr. Anderson says.

According to Dr. Anderson, the reasons for the chronicity in patients with chronic contact dermatitis can be due to an incorrect diagnosis or a failure to identify the contactant.

Covering the bases

When evaluating a patient with contact dermatitis, the physician should always start with the standard tray (preservatives, fragrances).

This can be supplemented with aimed allergens based on history, location of dermatitis, occupation and hobbies of the patient, and plants and cosmetics if applicable.

"Cosmetics that are 'leave-on' products, such as moisturizers and lipsticks, can be patch tested as is. 'Wash-off' products, such as shampoos and soaps, should be diluted to 1 percent. Industrial products must be handled with care when patch testing, and physicians should check the 'Fisher's Contact Dermatitis' book for proper dilutions," Dr. Anderson says.

In patients with facial rashes, the possible causes of the irritant and allergic contact dermatitis could be direct (cosmetic, medicine, grooming aid, objects worn, photo, airborne) or indirect (hands, person, pet) according to Dr. Anderson.

Preservatives are widely used in cosmetics, pharmaceuticals and industrial applications. According to Dr. Anderson, preservatives are the second-most-common cause of cosmetic allergic contact dermatitis.

"The hands, face, legs and axillae are common sites affected by allergic contact dermatitis to fragrances. Fragrances are the No. 1 cause of allergic contact dermatitis to a cosmetic ingredient. When patch testing, Balsam of Peru and Fragrance Mix are used to screen for fragrance sensitivity," he says.

Nickel is present in many metal alloys and is the most common allergen in patch test clinics. Here, a dimethylglyoxime test is administered.

According to Dr. Anderson, it is controversial whether the oral ingestion of nickel can cause a flare of nickel contact dermatitis.