Diagnostic test that identifies the substance causing contact dermatitis using standard allergens applied to the skin. Patches placed on the back are read after 48 hours.
Indication
- Recurrent or chronic hand or facial dermatitis
- Contact dermatitis developing after occupational exposure (hairdresser, healthcare worker, construction)
- Suspected reaction to cosmetics, perfume, or hair dye
- Investigation of metal (nickel, cobalt) or latex allergy
- Suspected reaction to topical medication or wound care product
- Unexplained pruritic eczematous presentation
Preparation
- Topical corticosteroids should not be used at the test site (usually the back) for at least 1 week prior
- Doses of systemic corticosteroids or immunosuppressants should be reviewed with the physician
- Avoid showering, applying creams, or sun exposure on the back 24 hours before testing
- Hairy backs may need to be shaved if necessary
- Sweating activities and intense exercise should be avoided throughout the test
How it's performed
- Allergens, primarily from the standard European series, are prepared on small adhesive patches
- Patches are placed on the back in regular rows and the layout is mapped
- The patient continues daily activities for 48 hours while keeping the patches in place
- First reading is performed 30 minutes after the patches are removed at 48 hours
- Second reading is repeated at 72-96 hours; some allergens may require a 7-day reading
- Reactions are graded according to international ICDRG criteria
Post-procedure
- An avoidance list and daily-life alternative recommendations are provided for positive allergens
- Coordination with the workplace physician is recommended for occupational allergens
- Dark skin discoloration at the test site fades within weeks
- Repeat testing or use testing may be planned for borderline reactions
- Topical treatment is arranged if the reaction persists
Risks
- Itching, redness, and burning sensation at the test site (expected reaction)
- Blistering and temporary discoloration in severe reactions
- Very rarely, systemic reaction and exacerbation of existing eczema
- Temporary irritation from the patch adhesive
FAQ
What is the difference between patch test and prick test?
Patch test investigates delayed-type (cellular) contact allergies and requires 48-96 hour readings. Prick test evaluates immediate-type (IgE-mediated) food and respiratory allergens.
Can I shower during the test?
The back should not get wet while the patches are in place. After the patches are removed, you can shower gently at the time recommended by your physician.
When are the results finalized?
Although the first reading is at 48 hours, some allergens may produce reactions at 72-96 hours or even on day 7. Therefore, multiple readings are scheduled.
Is a positive result lifelong?
Contact allergies are usually permanent; however, with long-term avoidance of the allergen, skin findings can be controlled.
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