Patch Testing
Specialized testing for contact dermatitis and delayed hypersensitivity reactions.
Overview
Patch testing is used to diagnose contact dermatitis, a delayed hypersensitivity reaction that occurs 24-72 hours after skin contact with an allergen.
contact Dermatitis
description
Inflammatory skin condition caused by direct contact with allergens or irritants
types
allergic
Immune-mediated reaction to specific allergens
irritant
Non-immune reaction to irritating substances
common
- Nickel (jewelry, metal objects)
- Fragrances and preservatives (cosmetics, personal care products)
- Rubber chemicals (gloves, shoes)
- Formaldehyde (various products)
- Plants (poison ivy, oak, sumac)
process
preparation
- Small amounts of potential allergens applied to patches
- Patches placed on back (usually)
- Left in place for 48 hours
- Avoid getting area wet or sweaty
reading
- First reading: 48 hours after application (patches removed)
- Second reading: 72-96 hours after application
- Delayed reactions may appear later
- May need additional readings
timeline
day1
Patches applied
day2
Patches removed, first reading
day3to4
Second reading (most important)
day5to7
Additional reading if needed for delayed reactions
interpretation
positive
- Redness, swelling, or blisters at test site
- Indicates allergy to that substance
- Reaction typically appears 48-96 hours after application
negative
No significant reaction - likely not allergic to that substance
relevance
Must correlate with patient's exposure history and symptoms
avoidance Guidance
identification
Once allergens are identified, comprehensive avoidance guidance is provided
sources
- Education about where allergen is found
- Product ingredient lists to check
- Alternative products that don't contain allergen
- Cross-reactivity information
resources
- Product databases
- Ingredient lists
- Substitution recommendations
- Follow-up support
preparation
- Stop topical steroids on back 1 week before
- Avoid sun exposure to back
- Back should be free of rashes
- Discuss all medications with provider
after Care
- Mild reactions are normal and expected
- Avoid scratching test sites
- Follow provider's instructions for care
- Keep test sites dry until final reading
Ready to Get Started?
Schedule a consultation to discuss your specific needs and create a personalized treatment plan.