Last Updated on October 29, 2023
A patch test is a method used to determine if a specific substance causes inflammation of the skin. It is often used to test for allergens.
The Procedure of Patch Test
On the first visit, tiny quantities of 25 to 150 materials (allergens) in individual square plastic or round aluminium chambers are applied to the upper back. They are kept in place with special hypoallergenic adhesive tape. They are kept in place undisturbed for at least 48 hours.
At the second visit, usually two days later, the patches will be removed. and the back is marked with an indelible black felt tip pen or other suitable marker to identify the test sites.
These marks must still be visible at the third visit, usually two days later (4 days after application). The back should be checked and if necessary, remarked on several occasions between the 2nd and 3rd appointments.
The result for each test site is recorded. It can be
- Negative (-)
- Irritant reaction (IR): Irritant reactions include sweat rash, follicular pustules and burn-like reactions.
- Equivocal/uncertain (+/-): Uncertain reactions refer to a pink area under the test chamber.
- Weak positive (+): Weak positives are slightly elevated pink or red plaques.
- Strong positive (++): Strong positives are papulovesicles.
- Extreme reaction (+++): Extreme reactions are blisters or ulcers.
The relevance of the test depends on the site and type of dermatitis and the specific allergen.
If the result is positive, the person is probably allergic to that substance(s).
The most frequent allergen that was recorded in many research studies all around the world is Nickel.
