Testing for Detergent Allergies
Patch testing, not prick testing, is the appropriate method for evaluating suspected detergent allergy, as detergents cause delayed-type hypersensitivity (allergic contact dermatitis) rather than immediate IgE-mediated reactions. 1
Why Patch Testing (Not Prick Testing)
Patch testing is the gold standard for diagnosing allergic contact dermatitis from detergents, which involves type IV delayed hypersensitivity reactions mediated by T lymphocytes, not IgE antibodies 2, 3
Prick testing is inappropriate for detergent allergies because it evaluates immediate IgE-mediated reactions (type I hypersensitivity), which is not the mechanism by which detergents cause dermatitis 2
However, if you suspect contact urticaria (immediate reaction with hives upon detergent contact), then open patch testing or repeated open application testing on the forearm may be useful, with readings at 30-60 minutes 1
Available Testing Approaches for Detergents
Standard Patch Testing Series
Standard baseline screening series (which picks up approximately 80% of allergens) includes common detergent components like fragrances, preservatives, and surfactants 1, 4
The baseline series does not typically include complete detergent formulations, but tests individual allergenic components found in detergents 1
Testing Patient's Own Detergent
Patients' own detergent products should be patch tested at non-irritant concentrations when suspected as the cause 1, 4
For laundry detergents specifically, 0.1% aqueous dilution has been used in research studies to minimize irritant reactions while detecting true allergic responses 5
Testing should be performed using proper patch test chambers (such as Finn chambers) applied to the upper back for 48 hours, with readings at day 2 and day 4, and ideally a third reading at day 7 1
Important Clinical Context
Detergent Allergy is Rare
True allergic contact dermatitis to detergents is extremely uncommon, with one multicenter study finding only 0.7% (5 of 738) dermatitis patients had positive reactions to laundry detergent, and even among these, some reactions were likely irritant rather than allergic 5
Irritant contact dermatitis from detergents is far more common than allergic contact dermatitis, caused by the surfactant properties and frequent wet work exposure 1
Distinguishing Allergy from Irritation
Because detergents are inherently irritating, differentiating true allergic reactions from irritant reactions on patch testing can be challenging 5
Repeated open application testing (applying the diluted detergent to the forearm twice daily for up to a week) can help distinguish allergic from irritant reactions 1
Testing should include an irritant control (such as 0.1% sodium lauryl sulfate) to help interpret positive reactions 5
Practical Testing Protocol
When evaluating suspected detergent allergy:
Apply standard baseline patch test series to screen for common allergens in detergents (fragrances, preservatives, surfactants) 1, 4
Add the patient's specific detergent at 0.1% aqueous dilution using proper patch test chambers 5
Include an irritant control (0.1% sodium lauryl sulfate) to help interpret results 5
Read at days 2,4, and ideally day 7 to capture delayed reactions 1
If positive, perform repeated open application testing to confirm clinical relevance and distinguish from irritant reactions 1
Common Pitfalls to Avoid
Do not assume all detergent-related dermatitis is allergic—irritant contact dermatitis from frequent handwashing, wet work, and surfactant exposure is much more common 1, 5
Avoid testing during active widespread dermatitis or within 6 weeks of UV exposure, as this increases false-negative rates 4, 6
Do not test at full strength—undiluted detergents will cause irritant reactions in most patients, obscuring true allergic responses 5
Remember that positive patch tests only indicate sensitization, not necessarily clinical relevance—correlation with the patient's actual dermatitis pattern and exposure history is essential 1