What is Allergic Contact Dermatitis? And why is my dermatologist recommending that I receive allergy patch testing?

Allergic Contact Dermatitis is a very specific type of allergy that occurs in the skin, and can mimic other rashes such as eczema, a drug reaction, or an irritant contact dermatitis. Sometimes, the allergic contact dermatitis covers large areas of skin, but other times it is localized to only the hands (or one single hand), the eyelids or the underarms. On biopsy, allergic contact dermatitis can mimic the pathology of eczema but the location of the rash can better delineate one condition from the other.

Once your doctor has given a presumed diagnosis of Allergic Contact Dermatitis, it is necessary to proceed with a very specific type of testing called patch testing. Patch testing is actually specific to the specialty of dermatology. Allergists typically do not perform this type of testing. When it comes to allergies, there are several different types of allergic reactions.

The Allergic Contact Dermatitis is considered a Type IV or delayed type of allergic reaction. When the skin comes into contact with something, there are cells that are messengers that begin to send signals to other cells located inside of the body. Once the immune system determines whether it is something that is OK (and thus no rash) or it is not OK, a subsequent rash can occur. Location is not always an easy way to determine what the contact allergen is. Why? If someone has an eyelid dermatitis, it is necessary to perform patch testing before determine what exactly is causing the rash. Most people would assume it is something they are putting on their face, or scalp or the eyelids themselves. Sometimes that is true. Other times, it is an issue of transfer from the hands, which touch so many things in the course of a day, and then a rash occurs only on the delicate eyelid skin, and not on the more robust skin of the hands.

Many times, patients try to determine their allergy by process of elimination. Due to the delayed nature of the Allergic Contact Dermatitis, it is impossible to know when or what contacted the skin in the days prior to the actual rash erupting. Additionally, even if a patient has not intentionally changed anything in their environment, it does not mean the detergent or body wash they have used for years has not suddenly had a change within the ingredient list by the manufacturer. It also does not take into account the possibility that the ever-changing immune system has changed yet again, and now produced an allergy where none existed previously.

The types of allergens that are being tested on the patch testing is a list of chemicals and metals which manufacturers are frequently using, and which seem to have a high allergic sensitivity conversion in the general population. The list of allergens are updated yearly by the Society of Allergic Contact Dermatitis, as the potential list of allergens numbers in the few thousand range, but realistically, dermatologists cannot test for 2,000-3,000 allergens. Instead there are typically between 48-80 allergens that are selected as being the most common to which people can react.

Patch testing, like its allergy type, is delayed. The patches of allergens are placed, typically on the back, and the patient is allowed to return to daily living while avoiding excessive sweating or direct water contact with the patches to ensure that the patches stay in contact with the skin for typically 48 hours in duration. When the patient returns to clinic, the patches are removed and it is determine whether there is positivity to any of the allergens. If a positive reaction is found, information can be given that correlates to the positive allergen, the multiple names that it goes by, as well as common product categories in which the allergen may be found. The list given to patients is by no means exhaustive. And, if a positive reaction is found, the real work for the patient begins in order to completely eliminate that allergen from both their home and their work environment.

Even beyond the office visit at 48 hours, the patch test may produce an even more delayed positive response at 72 or 96 hours. I have seen a latent positive reaction as far out as 8 days after the patches were placed on the back, and then removed at 48 hours. Without patch testing in the face of presumed or biopsy proven Allergic Contact Dermatitis, it is impossible to determine what the offending allergen is due to the delayed nature of the reaction. I have made the mistake of trying to assume it is “x” when it is actually “y” based on history and rash location and duration. Wrong! One particular patient who comes to mind suffered from an eyelid dermatitis. She also enjoyed eyelash extensions, and was quite concerned when she presented to me that her dermatitis was related to her lash activities. Once patch testing was performed, it was evident that it had nothing to do with false lashes, adhesives or anything else related to her eyelash extensions, but rather her allergy was to a preservative commonly found in hand sanitizers. She was not allergic to EVERY hand sanitizer–only certain ones. Her employer had provided her with a variety of hand sanitizers based on the cost of the sanitizer at the time of purchase. Once she changed her sanitizer to one that did not contain her particular allergen–no more eyelid dermatitis!

If patch testing cannot take place due to patient’s perception that they know best, or the physician is performing an unnecessary procedure for monetary gain, I liken it to the following example. If your car that is making an unusual noise or not running correctly, and you take it to a mechanic, you cannot mandate they fix it unless they are able to run diagnostic tests and look under the hood. If you have a presumed Allergic Contact Dermatitis, by not allowing proper patch testing by a dermatologist, you are not allowing that clinician to properly assess and advise the proper treatment. In this case, the proper treatment, and the best treatment is avoidance of the known allergen. Avoidance of known allergens will negate the need for costly and unnecessary medications and doctor’s visits in the future.