Allergic Contact Dermatitis

Allergic Contact Dermatitis

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Allergic contact dermatitis is an itchy, red rash caused by direct contact with an allergen. Sometimes, the rash may develop as dry, scaly, or cracked skin, and bumps and/or blisters may also form. In most cases, common substances like fragrances, metals (in jewelry), soaps, cosmetics, and plant matter are the cause of this type of dermatitis.

While allergic contact dermatitis is neither contagious nor life-threatening, it can be very uncomfortable, especially if an individual does not know its cause. To successfully treat this type of dermatitis, you will need to identify (and, subsequently, avoid) the cause of the reaction. Skin allergy testing is used to determine which allergens cause allergic contact dermatitis. Depending on the results, the patient will know to either avoid certain chemicals or will be prescribed a medication.

Allergic contact dermatitis is one of several forms of dermatitis that can appear. Irritant contact dermatitis, for example, can cause similar but slightly different symptoms like swelling, blistering, extreme dryness, and open sores. Irritant contact dermatitis happens when the skin comes into contact with a toxic material—not just an allergen. This can include bleach, battery acid, kerosene, some detergents, pepper spray, and other harsh chemicals.

Allergy Patch Testing

Allergy patch testing is a method of identifying allergenic triggers, especially those with a delayed reaction. This test can determine whether a substance is causing an allergic skin irritation, also known as contact dermatitis. Patch tests usually require two or more trips to the doctor. You will need to wear a patch for about 48 hours to get the best results for determining the nature and severity of your allergic reaction.

During this type of skin allergy test, patches with different suspected irritants, also known as allergens, are applied to a person’s back. The allergens will be suspended in small chambers that look like panels and are attached with hypoallergenic tape. These patches remain on the skin for around 48 hours and are then removed by a doctor. The dermatologist will then examine the skin for signs of a reaction. Typically, a standard set of allergens, which make up around 85% of all dermatitis causes, are used in allergy patch testing, but more specific materials may be used. The most common types of allergens include chemicals in hair dye, cosmetics, and medications.

Whether you think you have allergic contact dermatitis or irritant contact dermatitis, allergy patch testing is a great diagnostic tool. A patch test can help make a differential diagnosis if the cause of the dermatitis is unknown.


What symptoms is a patch test used to diagnose?

Allergy patch tests are used to diagnose contact dermatitis. The symptoms of contact dermatitis, a skin reaction, are wide-ranging, but most manifest as an uncomfortable rash. Below, we have listed some of the most experienced symptoms.

  • Blistering
  • Dry, flaky, scaly skin
  • Hives
  • Oozing blisters
  • Burning sensation
  • Sun sensitivity
  • Skin redness
  • Extreme itching
  • Swelling
  • Ulcerations
  • Cracking skin (from extreme dryness)
  • Skin that feels tight or stiff

Allergy patch tests are important for diagnosing a specific allergen or toxin. Without a test, a patient will not definitively know what substance is causing the rash. As a result, they are very likely to re-encounter the allergen, develop another rash, and continue a cycle of recontamination. In some extreme cases, continued exposure to an allergen can cause a more severe and dangerous reaction. If you suspect you have contact dermatitis, it is important to get tested sooner rather than later.


How accurate is allergy patch testing?

The accuracy of a patch test will vary by allergen and the intensity of the skin’s reaction. The strongest reactions are the most easily and accurately identifiable, but weaker reactions are more difficult to identify. Some reactions may need more time to develop, while others may need a bigger quantity of the allergen to have a noticeable effect. As a result, some patients undergo more than one round of allergy patch testing to identify the allergen. Steroids and topical medications can also impact test results, so tell your doctor if you have used these prior to testing.

According to the Contact Dermatitis Institute, as many as 6 out of every 10 people who have an allergy patch test will receive negative results (i.e. they are not allergic to the materials used). However, this does not mean the test is inaccurate; instead, a negative result indicates that the specific allergen may not have been included in the initial sample. There are several thousand known allergens, and based on your symptoms, health history, environmental exposure, and results to the initial allergy patch test, a dermatologist can make a more tailored recommendation for a follow-up test. A positive allergy patch test result can also indicate a variety of outcomes.


How does allergy patch testing work?

Knowing what to expect with an allergy patch test can be difficult. This procedure involves attaching several containers full of allergens to the skin’s surface, often with hypoallergenic tape. Your dermatologist will place an allergen on your skin, place a small, plastic or aluminum container over it, and secure the container to your skin. The allergen is then left for at least 48 hours to allow potential contact dermatitis to develop. These dishes or panels are generally arranged in rows across the skin for easy identification after the 48-hour period. At the end of the test, the doctor will remove each dish and examine the underlying skin for signs of a rash or reaction.

Typically, this type of skin allergy test is conducted on a person’s back, as this provides the largest, most uniform patch of skin. While this may impact some daily choices, like sleeping position, the tightness of your shirt, and the way you sit, most doctors agree that this is the easiest part of the body to conduct the test.


What allergens are on a patch test?

Most often, the type and number of allergen extracts used in a test will be chosen by your dermatologist. They will ask a variety of questions regarding potential exposure (what brand of personal hygiene or cosmetic products you use, your occupation, your environment) to determine which set of allergens is most likely causing your reaction.

However, there are two separate types of TRUE patch tests approved by the FDA: The TRUE Test, which is used to test sensitivity to one or more of 35 allergens and mixes, and the Rubber Panel TRUE Test, which is used to diagnose allergic contact dermatitis for those who may be sensitive to one or more of the 5 rubber mixes. The former tests allergens like nickel sulfate, wool alcohols, parabens, epoxy resin, and Bacitracin. The latter tests rubber materials, like black rubber mix, Mercapto mix, thiuram mix, and Mercaptobenzothiazole.

In most cases, a standard or baseline series of allergens will be recommended, as they are the most common and important allergens that cause dermatitis. This baseline series will vary depending on where you are getting this skin allergy test, but they typically include any number of the 35 allergens used in the TRUE Test mentioned above.

Ultimately, though, you and your dermatologist will decide which allergens are mostly likely to be causing your reaction.


What are the most common types of allergic contact dermatitis?

Allergic contact dermatitis has many causes, but some are more common than others. When the skin encounters an allergen, the body triggers an immune system response, making the skin dry, itchy, and irritated. Some of the most common allergens include substances found in:

  • Jewelry (nickel)
  • Antibiotics
  • Sunscreen
  • Tattoo ink (permanent and temporary tattoos)
  • Rubber products, like latex
  • Poison ivy and poison oak
  • Preservatives
  • Fragrance
  • Chemicals found in perfumes, skin care products, and cosmetics
  • Certain foods, like peanuts and shellfish

When you schedule an allergy patch test, your dermatologist will ask questions about your use of the above products. This will help them narrow down which allergens may be causing the reaction. 

The American Contact Dermatitis Society votes on the “Allergen of the Year” every year. The “award” is designed to draw attention to allergens that may be very common, under-recognized, or that merit additional attention because they cause a significant or severe reaction. In the past few years, allergens to receive this award have included Cobalt, Methylisothiazolinone (used in many cosmetics and lotions), Neomycin (an antibiotic), and fragrance.


Visiting West County Dermatology for Your Allergy Patch Test

Allergy patch testing may sound like an intense process, but it takes just a few days to get results. If you experience chronic skin allergies but can’t determine their cause, a non-invasive test like this is well worth the effort of visiting a clinic three times. Plus, our convenient location and proximity to St. Louis means we can work with your schedule to provide a service that is convenient for you.

Once you receive a diagnosis, we have a variety of contact rash treatment options to help develop an allergy treatment and maintenance plan that works for your lifestyle. Contact us to schedule an appointment.