The epicutaneous test is a test procedure that can be used to detect and discover contact allergies. Often, the epicutaneous test is also called the patch test or patch test because patches are applied to the skin for up to two days. The epicutaneous test is recommended only for late-type contact allergies.
What is an epicutaneous test?
Epicutaneous test is a test in which various substances that may cause allergy are applied to the skin. The application is done with the help of special patches. Epicutaneous test is a test in which various substances that may cause allergy are applied to the skin. The application is carried out with the help of special plasters. The epicutaneous test is intended exclusively for the detection of allergies of the late type and therefore differs from other skin tests for the detection of allergies (such as prick test, prick-to-prick test, friction test), in which a reaction is expected after 20 minutes instead of after 72 hours as in the epicutaneous test. Epicutaneous testing is a standard procedure for suspected contact allergies.
Function, effect, and goals
If eczema, redness or the formation of wheals should occur during contact with various materials, whether at work or even in private life, an epicutaneous test is performed by the attending dermatologist or allergist. Before starting the epicutaneous test, the patient’s skin in the test area, which is almost always the back, must be free of oily substances such as creams and body lotion. First, the selected substances are placed in the chambers of a special patch. If many substances are to be tested at the same time, several patches can be used. Then, if necessary, the patches are fixed to the back with adhesive strips to avoid loosening and shifting of the patches, which could lead to falsification of the test result. The patches are left on the patient’s back for 48 hours. The patient must not shower or bathe for the duration of the epicutaneous test and must ensure that their back or the selected skin area does not come into contact with water or other substances. Sweating should also be avoided. After 48 hours, the patches are removed and marks are made on the back with a pencil so that a correct evaluation of the epicutaneous test can be made later. Approximately one hour later, the first reading is taken. If an allergic reaction is present, there should have been reddening of the skin, formation of vesicles or wheals, or other signs of an allergic reaction in the area of a particular patch chamber. At least one more reading is taken after another 24 to 48 hours. If contact allergy is present, the skin condition at the affected site(s) should have worsened. The epicutaneous test is completed after the second or, if necessary, third reading if there is still uncertainty after the second reading. Recommendations for epicutaneous test series are published by the DKG, the German Contact Allergy Group. It is recommended to test the standard series in every patient with possible contact allergy. The standard series includes nickel and various fragrances, which are very common in cosmetics. Other test series in the epicutaneous test, for example, cover substances typically found in various occupations, such as substances in the construction trade or hairdressing substances.
Risks and side effects
Epicutaneous testing is a standard procedure in which complications or side effects are very rare. In the case of a very strong allergic reaction, the resulting skin reaction can also spread to neighboring skin regions. In addition, a so-called “angry back” can occur. In this case, the skin reacts at very many test sites. Surrounding skin may also be affected. Nevertheless, in such cases the patient does not have numerous contact allergies. Instead, a large proportion of the results are false positives because the skin of the back is itself irritated by the epicutaneous test. In such a patient, only a few substances should be tested at a time. Another problem with epicutaneous testing is reactions to materials used in the epicutaneous test. If a patient is sensitive to them, the skin areas that have come into contact with them will be red and irritated.In some circumstances, this may prevent evaluation of the epicutaneous test.
