Patch Testing

What is Patch Test?

Contact Allergy and ACD

At Metroderm DC in downtown Washington DC, a patch test will determine if your skin condition is caused by allergic reactions to haptens.

The eczema, flaking skin or blisters you are experiencing may be symptoms of Allergic Contact Dermatitis (ACD). ACD is a disease of the skin that emerges in people with Contact Allergy.

Contact allergies develop over time by exposure of the skin to Haptens. With increased exposure of a certain hapten the likelihood of developing a Contact Allergy increases. The threshold of how much exposure of a hapten one can endure before developing contact allergy is individual and varies greatly from one person to another.

Haptens are small, chemically reactive, molecules that binds with the proteins in your skin – eliciting immune responses. Haptens can be found in all sorts of products such as jewelry, makeup, perfume, shampoo, clothing or preservatives in work related products.

How does Patch Testing work?

The test procedure for diagnosing Contact Allergy will involve a number of visits at a clinic within a one-week time frame. After an initial consultation with your physician a patch test will commence. The test consists of a set of patch test units containing small amounts of suspected haptens being applied to your back. The Patch Test Units are designed to provide ideal for the haptens to interact with your skin.

After two days the patch test units will be removed by your physician and, depending on the haptens tested and on your skin type, one or more return visits will follow for skin reading (interpretation).

Precautions

Any medication altering the immune system (e.g cortisone and antihistamines) cannot be used during the test period.
Depending on the Patch Test Units used, showers, bathing and exercise may have to be avoided – ask you physician for directions.
Do resist the urge to scratch your back during the test.
Don’t expose your back to sunlight for the duration of the patch test.

FAQ

Q: How is Allergic Contact Dermatitis treated?

A: There is no cure for Contact Allergy. Topical steroid creams and ointments may reduce the itchiness of the rash caused by contact allergies, but the only way to stay clear of Allergic Contact Dermatitis is to altogether avoid the hapten that is causing the eczema.

Q: How do I look for haptens in products?

A: Make a habit of always reading the list of ingredients of products that you are using. Memorize the chemical name as well as possible trade names of the hapten that you are looking for. Possible synonyms for each haptens are available in our database. Remember that terms such as “unscented” and “hypoallergenic” are unregulated and are not equal to “fragrance free” and “will not cause allergies”.

Q: A previous Allergy Test showed no allergic reaction, could I still have Contact Allergy?

A: Yes. Although the name suggests otherwise, Allergy Testing (Prick Testing / Intradermal Allergy Testing), does not test for skin allergies (contact allergies) but for food and respiratory allergies. Contact allergies can only be diagnosed by Patch Testing. Q: Will my Patch Test results show if I am allergic to pollen, foods and pets? A: No. As Patch Tests do not work in the same way as Allergy testing (Prick Testing / Intradermal Allergy Testing) a Patch Test can not test for respiratory allergies.

Q: Is my skin condition Allergic Contact Dermatitis?

A: A possibility of Allergic Contact Dermatitis (either as a sole skin problem, or complicating another skin disease) should be considered if:

Your dermatitis/eczema always (or frequently) becomes aggravated after a skin contact to particular objects (e.g. a pen, toy, shoes) or substances (e.g. hand cream, perfume, metal working fluid at your work etc.)
Your dermatitis/eczema is restricted to, or more pronounced in the areas of the body that were in most contact with the given object or substance.
Your dermatitis/eczema clears or improves during holidays, and relapses after returning back to your home or work.
Your dermatitis/eczema is mainly located on the hands, around the eyes, or in the genital area.
Your dermatitis/eczema lasts longer than 3 months, even if another diagnosis has already been established (other chronic inflammatory diseases of the skin may enable the penetration of sensitizers and promote sensitization).

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