Dermatology• Updated 21 October 2026
Patch Test
A test that finds substances causing allergic skin reactions (contact dermatitis).
Results: Read after 2 and 4 days
Quick Summary
Primary Purpose
To identify allergens such as nickel, fragrances, hair dye and preservatives.
What It Measures
Skin reactions to small amounts of allergens.
Preparation
Avoid steroid creams on the back and keep it dry during the test.
Overview
Patches stay on the back for 48 hours.
It's different from a skin prick test for hay fever.
What It Measures
Skin reactions
Red, itchy areas under patches.
How It's Performed
- 01
Apply
Patches on the upper back.
- 02
Keep dry
For 48 hours.
- 03
Read
At 2 and 4 days.
Interpreting Results & Next Steps
Discuss with Doctor
Your doctor will explain what your result means and what happens next.
If values are High:
Positive reactions show what to avoid.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Allergy Skin Test(opens in a new tab) · MedlinePlus, US National Library of Medicine