Patch testing recommendations
Contact dermatitis is an inflammatory reaction caused by skin contact with substances to which you are allergic. These substances can be an ingredient in your perfume, shaving cream, ointment, metals, rubber boots, etc.
The patch test should be applied in a healthy area of skin, preferably in the upper back, left or right of the spine. It can also be applied to the outside of the arm.
The area where the test is applied must be free from dermatitis or other skin reactions.
Avoid sun exposure on the area where the test will be placed. It has been proved that ultraviolet rays can cause suppression of the reaction.
The application of topical corticosteroids on the area should be stopped two weeks before, as they can suppress the reactions of the test. The administration of oral corticosteroids may interfere with the results of the test and therefore they should be avoided for a week before testing.
For testing, each substance is mixed with vaseline and applied to the skin via a disc or patch of polyethylene and then taped to the skin in strips and left in place for two days.
A numbering system is used to identify each substance in each place and an adhesive strip is applied to prevent the patches coming off.
After 48 hours the patches are removed and the skin is examined to see if any reactions have appeared. After 96 hours, without the area being washed, a final reading is taken.
Copious sweating, which may affect adhesion, may interfere with the test results.
Therefore, physical effort or sport activities should be avoided as well as the application in the months of excessive heat.
You should keep the area dry. When showering or bathing, make sure the patch or the skin around it does not become wet. If it gets wet, it could come off and some of the substances could be eliminated.
If for any reason the patch falls off, it must be placed back in position quickly with the help of an adhesive strip.
The patient should notify the doctor of any delayed reactions, for example with nickel sulfate and p-phenylenediamine and medications that can cause reactions up to 4-5 days after testing.
Avoid scratching. If scratched, it may cause skin irritation and itch even more. If your skin turns red from scratching, it will be difficult to interpret the test results.
If the test shows you are allergic to any substance, the doctor will inform you where these substances are found.