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Allergic contact dermatitis is a skin condition characterized by irritation, dryness, blisters, redness, and swelling on the skin’s surface, which can cause pain and discomfort for the patient. While there are several types of dermatitis, including irritant contact dermatitis and atopic dermatitis, allergic contact dermatitis is a type IV hypersensitivity reaction, meaning that contact with an irritant has become triggering to the immune system, which causes an allergic reaction within 48-96 hours of contact with the skin. When looking to determine the cause of allergic contact dermatitis, the best type of allergy skin test to undergo is patch testing, which needs to be performed in the office of a board-certified dermatologist, such as Dr. Michele Green.

Patch testing is a type of allergy testing that involves the application of small amounts of allergens to the test site covered by patches of hypoallergenic tape. The patches are left on for 48 hours, which allows enough time for the potential allergen to cause an allergic reaction on the skin’s surface. Patch testing is best used for identifying the most common potential allergens, which frequently include different substances within preservatives, rubber antioxidants, nickel in jewelry, chemicals within antibiotics and topical steroids, and acrylates within nail cosmetics, adhesives, and hair extensions. With a patch testing allergy skin test, Dr. Green can determine the cause of an allergic reaction and take steps to develop a personalized treatment plan and prevention strategy to meet your needs best. The first step in eliminating allergic contact dermatitis is to schedule an initial consultation with experienced dermatologist Dr. Michele Green.

Expert board-certified dermatologist Dr. Michele Green has been treating patients in her Upper East Side New York City dermatology office for more than 25 years. Experienced in many medical and cosmetic treatments, Dr. Green is always on the cutting edge of the most effective treatment practices to promote the well-being of her patients. With her proprietary line of skincare products, MGSKINLABs, Dr. Green is a master at choosing lotions, creams, and ointments that will keep your skin healthy, moisturized, and smooth without causing any irritation. Well-known for high patient satisfaction, Dr. Green has been voted one of the best healthcare providers in New York City by such publications as Super Doctors, New York Magazine, and Castle Connolly.

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What is patch testing?

Patch testing is a procedure that tests for common allergens that can cause allergic contact dermatitis. Performed at a dermatologist’s office, patch testing involves the application of small concentrations of potential allergens in the form of many adhesive patches typically placed on the upper back. Patch testing is designed specifically to test for a type IV hypersensitivity reaction to a contact allergy, meaning an allergic reaction to substances that come into contact with the skin, leading to skin irritation known as dermatitis. Unlike other forms of allergy skin tests, such as skin prick tests (scratch tests), patch testing does not test for an immediate positive reaction at the test site. It can take several days for a skin reaction to occur with contact allergens, so the patch test is left on for 48 hours. Scratch tests are used to test for a variety of potential allergens, including airborne allergens, hay fever, drug allergies, and food allergies. An allergist or dermatologist may also perform blood tests to determine potential allergens. When testing for food allergies, it is important to avoid intradermal tests, as there is the potential for false negative results and a high risk of a severe allergic reaction, such as anaphylaxis. To find out which allergy test is best to meet your needs, schedule your initial consultation with expert board-certified dermatologist Dr. Michele Green.

What is Allergic Contact Dermatitis?

Allergic contact dermatitis is a skin irritation that occurs when different substances or chemicals come into contact with the skin. Characterized by red, itchy, blistered, swollen, dry, and bumpy skin, allergic contact dermatitis is a type of dermatitis that is caused specifically by an allergen. As studied by those in the field of immunology, allergic contact dermatitis occurs when the presence of an allergen on the skin’s surface activates the immune system, causing inflammation, irritation, and blisters on the skin’s surface. Allergic contact dermatitis can develop over time, known as the sensitization phase, for people who are frequently exposed to a certain chemical or substance, meaning that people might not react to the allergen for years before developing the allergy. The condition is known as a type IV hypersensitivity reaction, meaning that the irritation that develops on the skin’s surface occurs 48-72 hours after the skin has been exposed to the allergen.

Allergic contact dermatitis is one of several types of dermatitis, which includes atopic dermatitis (eczema) and irritant contact dermatitis. Atopic dermatitis (eczema) is a genetic skin condition that is caused by a weak skin barrier that fails to hold moisture within the skin, leading to cracked, dry, irritated, sensitive, bumpy, or blistered skin. Eczema skin rash can also be caused by an excess of the Staphylococcus aureus bacteria on the skin’s surface, which can also weaken the skin barrier and harm other bacteria. With a weakened skin barrier, the immune system can trigger an inflammation reaction, leading to the appearance of a rash. Irritant contact dermatitis, on the other hand, occurs without any prior immune system sensitization to the irritant that causes the rash, meaning the body has not developed an allergy to the product before the reaction takes place. This means that irritant contact dermatitis occurs immediately after exposure, as compared to allergic contact dermatitis, which takes several days to develop after exposure. Dr. Green can help you discover the type of contact dermatitis you are experiencing and generate a treatment plan that will best meet your needs.

How does allergy testing work?

If you suspect you are experiencing any form of dermatitis, the best first step is to schedule a consultation with an experienced dermatologist, such as Dr. Michele Green. Dr. Green will examine the affected area and recommend the type of allergy test that will be most likely to identify the potential allergen. If a patch test is recommended, the allergy test will be performed in the office. Dr. Green will begin by placing a small amount of allergen on your skin, usually the upper back, before covering each test area with hypoallergenic tape (patch). You will then be asked to leave the patches on for 48 hours, carefully avoiding picking at or scratching the patches, getting the area wet, or excessive sweating, as these activities can affect the test results. After 48 hours, you will be asked to return to Dr. Green’s dermatology office to have the patches removed. At this point, a reaction to any of the allergens placed on your skin indicates a positive patch test, and Dr. Green can tell you which irritants you are allergic to. Allergic contact dermatitis can take as many as four days to develop, and, as such, Dr. Green will ask you to return one more time after 96 hours to determine if any other positive patch tests have occurred. Based on these results, Dr. Green will then determine a treatment plan that will help you avoid future allergic reactions.

What are the most common allergens?

Skin allergies are the standard cause of allergic contact dermatitis and can come from a variety of triggers. Common triggers include:

  • Pet Dander
  • Pollen
  • Poison Ivy
  • Irritating fibers or fabrics
  • Extreme temperatures (cold or hot)
  • Detergents and soaps
  • Sunscreens and bug sprays
  • Metals (found on jewelry or used as buttons)
  • Certain chemicals and foods

Skin allergies typically manifest as allergic contact dermatitis but can also appear as hives or deep swelling in the dermis. If you think you may react due to a skin allergy, you can avoid items that likely caused the reaction and contact the office for further guidance.

What allergens are tested in a patch test?

Several different standardized patch tests exist that test for variations of the most common contact allergens, and the two most common in the United States are the T.R.U.E. test and the North American Standard Series.

The T.R.U.E. test assesses the following allergens:

  • Carba Mix from rubber antioxidant
  • Many potential allergens found in preservatives, including ethylenediamine dihydrochloride, thiomersal, Diazolidinyl urea, and imidazolidinyl
  • Hydrocortisone-17-butyrate found in topical corticosteroids
  • Bacitracin from topical antibiotics
  • Textile dye
  • Metal (gold)

Similarly, the North American Standard Series tests for the following common allergens:

  • Chemicals found in preservatives
  • Rubber antioxidant
  • Bacitracin from topical antibiotics
  • Fragrance Mix II found in many over-the-counter lotions, ointments, and soaps
  • 2-Hydroxy-4-methoxy benzophenone, which is a chemical found in most sunscreen
  • Ethyl acrylate, which is used in cohesive
  • Textile dye
  • Synthetic resin found in many nail cosmetic products
  • Triamcinolone acetonide found in topical steroids
  • Chemicals found in laundry detergent

While these are the standard patch tests that can detect many of the most common allergens, after your initial consultation, Dr. Green may choose to do a work-specific patch test depending on your career or hobbies. Certain fields, including hairdressers, nail technicians, and metal workers, are at a higher risk of developing allergic contact dermatitis. In these cases, Dr. Green may order Expanded Patch Testing, which tests for the most common allergens found at certain jobs.

What does patch testing test for?

Patch testing tests for an allergic reaction to the small amounts of allergens that are placed in patches across the upper back. Allergic contact dermatitis is a type IV hypersensitivity reaction. It can take several days for the rash or skin irritation to develop after the irritant has come into contact with the skin. For that reason, patch tests are left on for 48 hours, and patients are expected to come in for a follow-up appointment 96 hours after the patches are initially applied. The most common contact allergy, affecting 18.5% of all patients who undergo patch testing, is nickel, which is commonly found in jewelry. Fragrances, which are most frequently found in perfumes, soaps, lotions, cleansers, and household products, are also incredibly common, triggering some form of reaction in 87% of all dermatitis patients. Dr. Green advises that patients experiencing contact dermatitis should also look for products labeled as “fragrance-free” rather than “unscented,” as “unscented” products may still contain fragrance mix. Many patients also experience skin irritation due to preservatives, hair dye products containing paraphenylenediamine (PPD), rubber gloves, nail cosmetics, and topical medications, such as steroids and antibiotics.

Where should a patch test be performed?

Patch tests should be performed in the office of an expert board-certified dermatologist, such as Dr. Michele Green. Receiving the patch test from a trained healthcare provider is essential to achieving the proper results. Once the allergy test has been performed and the test results collected, Dr. Green will also create a treatment plan to help patients avoid allergens in the future and prescribe products that can help reduce the irritation due to a current allergic contact dermatitis rash.

Where should a patch test be applied?

Patch tests are typically applied to the upper back, which provides a large surface area of hairless skin on which to place the small amounts of allergens and hypoallergenic tape. Once the patches have been applied, patients are advised not to pick at or scratch the patches, as these actions can affect the test results. With the patches placed on the upper back, patients are less likely to pick at the patches absent-mindedly. Patients should also keep the patches dry for the full 48 hours that they are on and avoid excessive sweating for 96 hours after the patches have been applied. Strict sun avoidance during patch testing is also essential to achieve accurate test results and reduce additional irritation.

How to prepare for your skin patch testing visit

The first step for preparing for patch testing is to schedule an initial consultation with board-certified dermatologist Dr. Michele Green, who will examine the affected area and ask about your recent interactions with potential allergens. Certain medications can interfere with the test results, which Dr. Green may advise stopping in advance of the exam, including antihistamines, asthma medications, anti-depressants, and heartburn medications. It is important to consult with your healthcare provider before stopping any medications.

How long does a patch test take?

Patch testing will require three visits to Dr. Green’s office to complete effectively. During the first visit, Dr. Green will apply the patches of potential allergens to the skin, covering them with hypoallergenic tape. These patches must be left on the skin for 48 hours and kept dry the whole time. After 48 hours, the patient will return to Dr. Green’s office, and Dr. Green will remove the patches from the skin. At this point, some allergic reactions may have occurred, but some allergic contact dermatitis reactions will not manifest for up to four days. For that reason, patients must return for a follow-up appointment 96 hours (four days) after the initial patch test application. At this appointment, Dr. Green will fully determine the allergens responsible for allergic contact dermatitis in the patient.

Is patch testing uncomfortable?

Patch testing involves the application of small amounts of allergens on the upper back that are covered and left on the skin for 48 hours. Patients who are allergic to these allergens may experience an allergic reaction, which can manifest as itchy, irritated, raised, red, or swollen skin at the test site. For some patients, this can cause discomfort for the duration of the test, but patients must refrain from itching or picking at the patches. Following the procedure, Dr. Green may prescribe topical creams or ointments that can reduce the symptoms of the allergic reaction.

What is a patch test for hair?

Many hair dyes contain a common allergen called paraphenylenediamine (PPD), which can trigger a serious allergic reaction on the face and neck when applied to the hair. For that reason, hair dye will often come with instructions for how to test the hair dye on your skin before applying it to your head. This type of allergy test is known as an open application test, as you apply a small amount of the potential allergen to your skin and leave it uncovered for 48-72 hours. If your skin reacts to the product, you are likely allergic to the product and should not use it. 48-72 hours before dying your hair, follow the open application allergy testing instructions on the hair dye box to determine if you are allergic.

How to patch test skincare

If you are prone to allergic contact dermatitis, it may be best to do an allergy test for new skincare products before use. You can allergy test skincare products at home using a method called “open application testing,” which follows a similar principle to patch testing only without covering the allergen with a patch. Open application testing is most effective on skincare products like moisturizers, lotions, and creams but can be used for shampoo, cleansers, and soaps as well. To conduct an open application test on skincare products, apply a small amount of the skincare product to a hairless area of the body twice a day for one week. If you observe a reaction at the test site within that timeframe, it may be an indication that you are allergic to a chemical or fragrance within the skincare product. If you experience any sort of pain, swelling, redness, irritation, or blistering, it is best to avoid the product you tested.

How to do a patch test for skincare

To begin your open application testing for skincare products, start by identifying an area of skin that is smooth and hairless without any recent dermatitis (eczema) or sun damage. Then, apply a small patch of the skincare product (approximately 5 cm by 5 cm) to the test site twice a day for a full week. If you are testing a cleanser or a shampoo, wash the product off the test site about a minute after each application. If you experience an immediate reaction, you are likely experiencing irritant contact dermatitis rather than allergic contact dermatitis, meaning you do not necessarily have an allergy to the product. If you experience dermatitis within a few days of beginning the open application testing, it is likely that you are allergic to the product and should avoid its use. If you do react to the product, you can treat the skin irritation with a topical steroid.

Where to patch test skincare

Skincare products can be allergy tested at home using a method known as the open application testing method, which involves applying small amounts of the product to the test area without covering it. Open application testing for skincare products should be performed on a smooth, hairless area of the body that has not been recently affected by dermatitis or excess sun exposure. Typically, the best areas to perform open application testing are on the smooth side of the forearm or the inner elbow.

How long should you patch-test skincare?

If you are doing open application testing for skincare products at home, you should apply the product to your skin twice daily for one week. If you have not experienced a reaction from the product within one week, you are likely not allergic to the product. If you do experience an allergic reaction, you should avoid the use of the product. Allergic reactions can also indicate the need for a patch test performed by a board-certified dermatologist, who can tell you more specifically what you are allergic to and how to avoid those products in the future.

Where to patch-test face products

If you are performing an allergy test for facial skincare products at home, be sure to test those products on the arm or inner elbow before applying them to the face. If you have not experienced an allergic reaction to the product within one week, it is unlikely that you are allergic to the product, and you can begin using it on the face. Patients undergoing patch testing in the office of a board-certified dermatologist or healthcare provider, such as Dr. Green, will have their patch test performed on their upper back.

How to get started with patch-testing today

Allergic contact dermatitis is a skin condition in which certain products or chemicals trigger the immune system to produce an allergic reaction, which manifests as irritation on the skin’s surface. Characterized by an itchy, red, swollen, blistered, cracked, or dry rash, allergic contact dermatitis can cause major discomfort for patients, leading them to seek out the cause of their allergic reaction. The best method to test for potential allergens that cause allergic contact dermatitis is to undergo a patch test, which is a type of allergy test in which a small amount of allergens are placed on the skin and covered with a patch. The patch is left on for 48 hours to allow enough time for an allergic reaction to take place. After four days, Dr. Green will examine the skin reaction in the treated area to determine if any of the potential allergens yield a positive patch test. Patch tests must be performed in the office of an expert board-certified dermatologist, such as Dr. Michele Green, to yield the best results.

Experienced board-certified dermatologist Dr. Michele Green has been expertly treating patients in her Upper East Side New York City dermatology office for more than 25 years. A graduate of Yale University, Dr. Green is well known for her ability to create individualized treatment plans that meet each patient’s unique medical needs and aesthetic goals. When patch testing and treating allergic contact dermatitis, Dr. Green will generate the treatment plan and prevention program that will help keep your skin clear and rash-free. To find out more about patch testing and allergic contact dermatitis and to book an appointment, contact us online today or call Dr. Michele Green’s NYC-based office at 212-535-3088.

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