Contact dermatitis refers to inflammation of the skin caused by a substance that comes into direct contact with the skin. Irritation can cause immediate inflammation of the skin resulting in redness, itchiness or a burning sensation. An allergic reaction to a substance causes a delayed immune system reaction with similar symptoms. Allergic contact dermatitis is less common than irritant contact dermatitis.
A specialized form of testing in dermatology that evaluates if substances that come into direct contact with the skin may cause a delayed allergic reaction. This is different from allergy testing provided by an allergist that evaluates which inhaled or ingested substances may cause an immediate allergic reaction such as hives, swelling or anaphylaxis.
Eczema is synonymous with dermatitis. They both mean “inflammation of the skin.” The most common cause of dermatitis is due to a genetic predisposition and is called atopic dermatitis. People with atopic dermatitis often also have asthma and seasonal allergies (allergic rhinoconjunctivitis). When dermatitis is caused by things that touch the skin, we call that contact dermatitis.
An allergist/immunologist is a physician trained in providing, administering and interpreting skin prick testing. A skin prick test evaluates substances that may be inhaled (eg. dust, pollen, pet dander) or ingested (eg. food, medication) that cause an immediate hypersensitivity reaction such as hives, swelling or anaphylaxis. Patch testing evaluates substances that directly come into contact with the skin which may cause a delayed hypersensitivity reaction (dermatitis).
No. Dermatologists are trained to provide, administer and interpret patch testing. It takes 5 years of specialized training after medical school to become a dermatologist in Canada. Not all dermatologists offer patch testing, however, so it is important that you speak to your doctor or dermatologist in order to be appropriately referred.
We test to 80 of the most commonly identified allergens as suggested by the American Contact Dermatitis Society. For example, fragrances, preservatives, metals, rubbers, adhesives and dyes which are commonly found in personal care products or in the workplace are included. Your dermatologist will determine if additional screening allergens are required.
Typically, we place the patches on your back where there is enough surface area to apply the patches. The skin on your back is relatively immobile which helps keep the patches in place. If for any reason we cannot patch test you on your back, there are other areas of the body where the patches can be placed (i.e. upper arms, upper chest).
Patch testing will determine if you are allergic to something that your skin has come in contact with. Avoiding products with ingredients or substances you are allergic to may relieve your skin symptoms.
During the first visit the patches will be applied to your skin and must stay on for 48 hours. At the second visit the patches are removed and any reactions that may develop are recorded. Sometimes contact dermatitis make take a few days to manifest a reaction, therefore a delayed reading is required one week after the application of the patches.
No. In order to capture an accurate test, the back needs to be kept as dry as possible while the patches are in place. Sponge bathing is allowed, but you cannot shower, swim, soak in a tub or get excessively sweaty during the test. After the 48 hour reading, you may allow water to run down the back.
The initial consultation at Dr. de Gannes’ private office is the longest visit and lasts approximately 30 minutes. During this time, we gather information about your skin condition and provide information about patch testing. The actual patch testing occurs at St. Paul’s Hospital. Those visits last approximately 20 minutes (visit 1 & 3) and 5 minutes (visit 2). Depending on your test results, your visit 3 may be longer as we will provide you with information on allergen avoidance if necessary.
Often the less we use on our skin, the better! We recommend using bland cleansers and moisturizers. You may have some prescription ointments or creams that you can use, or some oral medication. Please talk to your dermatologist about whether or not these will interfere with your testing. You cannot proceed with patch testing if the skin on your back/upper arms is not clear or is actively inflamed with dermatitis.
True or False
FALSE – With allergic contact dermatitis the rash is usually delayed by one to two days, and may not appear for up to a week after contact.
FALSE – You can develop an allergy to a product even if you have been using it without problems for years. Also, products may change their ingredients over time but still retain the same name and packaging.
FALSE – Many products contain the exact same chemicals, preservatives, and fragrances etc. You may be exposed to your allergen in multiple personal care products.
FALSE – Many of these products contain fragrances, essential oils and preservatives all of which can cause allergic reactions.
TRUE AND FALSE – Rashes are usually most severe at the site of direct contact. However, substances may be transferred to other places on your body by your fingers or by rinsing or washing off the product.
FALSE – Even expensive products can contain allergenic substances.
TRUE – Food allergies present with hives, swelling of the tongue and face, difficulty breathing, abdominal pain, and diarrhea (symptoms of anaphylaxis). Food allergies are confirmed with skin prick testing by an allergist/immunologist, not by patch testing. Certain foods can cause irritation to the skin because of their acidity (citrus fruits, tomatoes). It is extremely rare for a food to produce true allergic contact dermatitis.