Treatments & Therapies

Patch test – treatment, effect & risks

Epicutaneous test

The epicutaneous test is a test procedure with which contact allergies can be detected and discovered. The patch test is often also referred to as a plaster test or patch test, since plasters are applied to the skin for up to two days. The patch test is only recommended for late-type contact allergies.

What is a patch test?

patch test is a test in which various substances that may cause allergies are applied to the skin.

The application is carried out with the help of special plasters. The patch test is intended exclusively for the detection of late-type allergies and therefore differs from other skin tests for allergy detection (such as prick test , prick-to-prick test, rub test), in which a reaction occurs after 20 minutes instead of 72 hours as expected with patch testing.

The patch test is a standard procedure when contact allergies are suspected.

Function, effect & goals

If contact with various materials, whether at work or in private life, should lead to eczema , reddening or the formation of wheals , the treating dermatologist or allergist will carry out a patch test .

Before starting the patch test, the patient’s skin in the test area, which is almost always the back, must be free of greasy 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 also be used. The plasters are then fixed on the back with adhesive strips, if necessary, to prevent the plasters from loosening and shifting, which could lead to a falsification of the test result. The patches are left on the patient’s back for 48 hours.

The patient must not shower or bathe during the patch test and must ensure that his back or the selected area of ​​skin does not come into contact with water or other substances. Sweating should also be avoided. After 48 hours, the patches are removed and markings are made on the back with a pen so that the patch test can be correctly evaluated later. The first reading is taken about an hour later.

If an allergic reaction has occurred, reddening of the skin, the formation of blisters or wheals or other signs of an allergic reaction should have occurred in the area of ​​a particular patch chamber. After a further 24 to 48 hours, at least one further reading is taken. If there is a contact allergy, the skin condition in the affected area or areas should have worsened. The patch test is finished after the second reading or, if there are still uncertainties after the second reading, the third reading.

Recommendations for epicutaneous test series are published by the DKG, the German Contact Allergy Group. It is recommended that the standard series be tested in each patient with possible contact allergy. The standard range includes, among other things, nickel and various fragrances that are very common in cosmetics . Other series of tests as part of the epicutaneous test cover, for example, substances that typically occur in various professions, such as substances in the construction industry or hairdressing materials.

Risks & side effects

The patch test is a standard procedure that very rarely leads to complications or side effects. 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. The skin reacts at many test points. Surrounding skin can also be affected. Nevertheless, in such cases it is not a question of a patient with numerous contact allergies. Instead, a majority of the results are false positives because the skin of the back is irritated by the patch test itself. In such a patient, only a few substances should be tested at a time.

Another problem with patch tests are reactions to materials used in the patch test. When a patient is sensitive to them, the areas of skin that have been in contact with them become red and irritated. Under certain circumstances, this can prevent the evaluation of the patch test.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.