SOS Allergo · I understand & manage
Patch tests: what should I do after application?
Removal after 48 hours, grid markings, photographs and delayed readings
Patch tests look for delayed allergy. The devices are usually removed after around 48 hours, but a reaction may appear several days later. Keep every scheduled reading appointment and monitor your back until the date given by the team.
The usual schedule
- Day 0
Patch application
Then - Day 2 — about 48 hours
Removal + first observation
Then - Day 3–4
Essential reading
Then - Around day 7
Late reading if scheduled
The exact schedule depends on the type of patch test and your centre’s protocol.
1. At 48 hours: remove the patches but keep the markings
After about 48 hours, the strips and chambers may be removed and discarded unless your team has asked you to bring them back. Chamber imprints or pressure redness do not necessarily indicate allergy.
The grid is essential: each square corresponds to a different allergen. If the lines fade, gently redraw them only if the team has asked you to do so. Do not recreate a completely lost grid from memory.
If the centre allows you to wash after removal, carefully avoid the tested area. Instructions provided by your department always take priority.
2. A reaction may appear late: photograph it
Even if your back looks normal on day 2 or 3, continue monitoring it. A positive reaction may appear later: infiltrated redness, papules, small blisters, itching or an eczema-like patch.
- Photograph the reaction as soon as it appears
- Take an overview of the back and grid
- Then take a clear close-up
- Use good lighting
- Keep the date and time
- Place a small ruler next to the lesion if possible
The photograph preserves the information. The appointment provides the interpretation.
3. Until the final reading
Avoid scratching the area, applying cream or a topical corticosteroid to the test sites without instructions, erasing the markings, exposing your back to sunlight or exercising hard enough to cause heavy sweating.
Day 2 — removal
What I observe · Photograph
Day 3–4
What I observe · Photograph
Day 5–7 / later
What I observe · Photograph
Key points
- Remove the devices at around 48 hours if instructed to do so.
- Keep the grid visible.
- Protect the area from water and sweating according to the centre’s instructions.
- Return for the scheduled readings.
- Photograph any delayed reaction.
Download the validated sheet
Keep this reminder with the instructions provided by your centre.
You may also want to read
Main references
- Uter W, et al. ESCD Guideline for Diagnostic Patch Testing - Update 2026. Contact Dermatitis. 2026.
- Johnston GA, et al. BAD guideline for contact dermatitis. Br J Dermatol. 2017.
- Barbaud A, et al. Skin testing with drugs in cutaneous adverse drug reactions. Contact Dermatitis. 2001.
Scientific review: September 2026 · sosallergo.fr