Guidelines for Patch Testing in Recurrent Dermatitis

Primary Diagnostic Approach

Patch testing with a standardized baseline allergen series is the primary laboratory investigation for recurrent dermatitis because clinical features alone cannot reliably differentiate allergic contact dermatitis from irritant or endogenous causes. 1
Offer patch testing to any patient with chronic or persistent dermatitis lasting more than a few weeks, as visual inspection cannot distinguish the underlying dermatitis type. 1
A baseline screening series detects approximately 80 % of relevant allergens, providing broad initial coverage. 1

The British Society for Cutaneous Allergy regularly updates its baseline series, removing obsolete allergens and adding emerging ones such as methylisothiazolinone. 2
When the baseline series fails to identify a culprit, add supplemental allergen series tailored to the patient’s exposure patterns (e.g., occupational chemicals, fragrances, rubber chemicals, cosmetics). 2
Test the patient’s own products at non‑irritant concentrations when specific products are suspected to be the source of dermatitis. 2

Defer patch testing for 3 months after discontinuing systemic immunosuppressive agents and for 6 months after stopping biological agents to prevent suppressed reactivity. 1

Standard readings are performed on days 2 and 4; adding an additional reading on day 6 or 7 when day‑4 results are unexpectedly negative captures roughly 10 % more positive reactions, including allergens such as neomycin and tixocortol pivalate. [1][2]
Readings should be conducted in natural daylight and graded as positive (+, ++, +++), negative, or irritant. 2
Metal salts (nickel, cobalt, potassium dichromate), fragrances, and carba mix frequently produce irritant reactions that can be misinterpreted as allergic positives; careful interpretation is required. 2

Perform photopatch testing when photoallergic contact dermatitis is suspected by applying a duplicate photo‑allergen series to the upper back, irradiating one side with 5 J/cm² UVA after 2 days. 2
True photoallergy occurs in < 5 % of cases, but additional readings after day 4 improve detection rates. 2

Use open patch testing for suspected irritants, contact urticaria, or protein contact dermatitis by applying the agent “as is” on the forearm with readings at 30–60 minutes and again at 3–4 days. 2
Repeated open‑application testing (applying the product twice daily for 5–10 days on the volar forearm) helps evaluate cosmetics and personal‑care products where irritancy may mask allergic responses. 2

The British Association of Dermatologists recommends patch testing for any patient with chronic or persistent dermatitis lasting more than a few weeks, as clinical features alone cannot reliably distinguish allergic contact dermatitis from irritant or endogenous causes 3, 4
The American Academy of Dermatology suggests patch testing for suspected allergic contact dermatitis based on history or physical examination findings, including disease aggravated by topical medications or emollients 5
Patch testing is recommended for previously well-controlled atopic or endogenous dermatitis that becomes difficult or impossible to control with the same topical treatments that previously worked 3, 4
The British Association of Dermatologists recommends patch testing for distribution patterns suggesting contact with specific items, such as marked facial/eyelid involvement or unusual patterns like sides of feet 5

The British Association of Dermatologists states that patch testing can be performed during pregnancy, but only when required and after informed consent is obtained, as no evidence of harm exists, but no safety data are available 3, 4
The British Association of Dermatologists recommends waiting 6 weeks after natural sun exposure or artificial UV exposure before patch testing to avoid false-negatives 3, 4, 6
A waiting period of 3 months after finishing systemic immunosuppressive agents is recommended before patch testing 3, 4, 6

The British Association of Dermatologists recommends a standardized baseline screening series, which picks up approximately 80% of allergens 7, 8
The American Academy of Dermatology suggests using an extended series for specific anatomical sites, occupational groups, and chemical exposures when the baseline series fails to identify less common allergens 3, 7
The British Association of Dermatologists recommends testing a patient's own products at non-irritant concentrations when suspected 7, 8

The American Academy of Dermatology warns against assuming all dermatitis is irritant or atopic without patch testing, as allergic contact dermatitis is at least as common in atopic dermatitis patients as in the general population 5
The British Association of Dermatologists advises against testing during active widespread dermatitis or on skin with recent UV exposure, as this increases false-negative rates 3, 4
The British Association of Dermatologists recommends remembering that positive tests only indicate sensitization, not necessarily clinical relevance, and correlation with active dermatitis and sometimes repeat open application testing is required for confirmation 5, 9