Contact Dermatitis And Skin Patch Testing

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skin patch testing

Spring is right around the corner, which means more outdoor activities for you and your family. Inevitably, someone chases after a ball thrown into the woods, or veers off the beaten path on a hike. Hours later their skin is covered with red itchy bumps and hives. This is a common reaction for many people during the spring and summer months. Contact dermatitis is an itchy rash that appears on your skin as a result of being exposed to a substance that you are allergic to. Poison ivy is one of the most commonly known causes and affects millions of people every year. There are also several common household substances that trigger contact dermatitis, including hair products, cosmetics, jewelry, laundry detergent, latex rubber and perfumes. Skin patch testing is one way to determine whether you are susceptible to contact dermatitis.

Just to be clear, skin rashes can occur from a multitude of responses, including heat, infections, medication and immune system disorders. For example, prevailing medical thinking is that eczema is not caused by an allergen. Rather, it is believed to be caused by a variety of factors, including but not limited to, genetics, environment, immune system irregularities and potential skin barrier defects. In any case, repeated skin rashes should always warrant a visit to a dermatologist or your general physician.

What Is Contact Dermatitis?

In contact dermatitis, an apparently harmless substance causes an immune system reaction when it comes into contact with the skin. Common symptoms in contact dermatitis may include:

  • Redness
  • Blisters
  • Itching
  • Rash
  • Hives
  • Burning

These symptoms can last for up to four weeks and can usually be treated at home through medications and topical creams. The best protection against contact dermatitis is to identify the specific triggers that cause reactions, so that patients can avoid these substances as often as possible.

A skin patch test can help determine the cause of an unknown dermatitis allergen. In fact, certain people may be allergic to more than one substance. The only way to narrow down the list is to conduct a skin patch test. Specifically, skin patch testing looks to identify items (specifically, chemicals) that are causing a direct adverse reaction to a person’s skin. A patch test does not require the use of any needles or injections.

What Is Skin Patch Testing?

Skin patch testing is a relatively simple procedure that can test up to over 200 allergens in some instances. First, a dermatologist will advise a patient of several simple, upfront measures to take, such as avoiding sunlight in the days leading up to the patch test. Next, at the dermatologist’s office, several patches will be taped onto the skin of a patient’s back. These patches each contain separate chemicals, which are left on the skin for up to 48 hours. The dermatologist will normally advise a patient to keep their back dry (no showers) and to avoid excessive sweating during this time. After two days, the patches are removed, and an initial reading is taken to check for any adverse reactions. The patient returns 24-48 hours later for an additional reading. A final analysis is completed, and the patient then resumes normal activities.

After the test, the dermatologist will rate any spots on the skin’s surface on a scale from “negative” to “extreme reaction.” Some extreme reactions may include blisters or ulcers on the skin, which will be treated immediately. Thereafter, the dermatologist will identify those substances which should be avoided by that patient to the extent they measured positive.

Tests For Other Allergens

Patch testing should not be confused with skin prick testing or blood testing for allergens. Again, patch testing looks to items (specifically chemicals) that contact the skin directly. Both skin prick and blood testing test for immunoglobulin E (IgE), which is an antibody specific to food allergies. Prick testing seeks to identify certain allergic reactions from airborne pollutants such as pollen, mold and pet dander. Finally, it should be noted that both blood and skin prick testing sometimes yield false positive results. For example, showing a positive reaction to all legumes (green beans, etc.) when the allergy only relates to peanuts.

Depending on the results of your patch test, a dermatologist may recommend either a skin prick and/or blood test to further identify any possible allergens.