Patch test

Of the Patch test is a test procedure with which contact allergies can be detected and detected. The patch test is often also referred to as a plaster test or patch test, as 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?

As Patch test is a test in which various substances that may trigger 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 in the patch test.

The patch test is a standard procedure for suspected contact allergies.

Function, effect & goals

If contact with various materials, whether at work or in private life, results in eczema, redness or the formation of wheals, the dermatologist or allergist treated will advise you Patch test carried out.

Before starting the patch test, the patient's skin in the test area, which is almost always the back, must be free of fatty substances such as creams and body lotions. First, the selected substances are placed in the chambers of a special plaster. Several plasters can be used if many substances are to be tested at the same time. The plasters are then attached to the back with adhesive strips, if necessary, in order 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 may not shower or bathe during the patch test and must ensure that his 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 plasters are removed and markings are made on the back with a pen so that the patch test can be evaluated correctly later. The first reading is taken about an hour later.

If there is an allergic reaction, there should have been reddening of the skin, blisters or wheals, or other signs of an allergic reaction 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 should have worsened in the affected area or areas. The patch test is finished after the second or, if necessary, if there are still uncertainties after the second reading, the third reading.

The DKG, the German contact allergy group e.V., publishes recommendations for patch test series. It is recommended that the standard series be tested on every patient with a possible contact allergy. The standard range includes nickel and various fragrances that are very common in cosmetics. Further test series as part of the patch test cover, for example, substances that are typically found in various professions, such as substances in the construction industry or hairdressing materials.

Risks & side effects

Of the Patch test is a standard procedure with which there are very few 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 to a large number of test sites. Surrounding skin can also be affected. However, in such cases it is not a patient with numerous contact allergies. Instead, the majority of the results are false positives because the skin on the back is irritated by the patch test itself. Only a few substances should be tested at the same time in such a patient.

Another problem with patch tests are reactions to materials that are used in the patch test. When a patient is sensitive to them, the areas of skin that came in contact with them are reddened and irritated. Under certain circumstances, this can prevent the patch test from being evaluated.