BACKGROUND: Sodium lauryl sulfate (SLS) has been included as an irritant control in the baseline patch test series of the German Contact Dermatitis Research Group (DKG) for two decades, although its diagnostic value remains controversial.

OBJECTIVE: To evaluate the strengths and limitations of SLS as an irritant control in patch testing.

METHODS: We retrospectively analysed data from 43 478 consecutive patients patch tested with 0.25% SLS aq. and 189 allergens within the IVDK network. SLS reactions were graded from 1 (weak) to 5 (strong). Associations between SLS reactivity and allergen-specific responses were examined.

RESULTS: Overall, 22.4% of all patients reacted positively to SLS, most with weak erythema (SLS 1). Stronger SLS reactions (SLS 2-5) were associated with male sex, age ≥ 40 years, occupational dermatitis and hand dermatitis. Positive SLS reactions correlated with several allergens of high irritative potential, notably cocamidopropyl betaine, formaldehyde, sorbic acid and diphenylguanidine. In contrast, plant-derived allergens showed weak or inconsistent associations. Importantly, grading SLS reactions (1-5) did not improve diagnostic discrimination compared to a simple positive/negative classification.

CONCLUSION: While SLS can indicate skin irritability for certain allergens, it is not a universal marker. Our large-scale analysis supports binary SLS classification and provides a robust evidence base for the ongoing debate on whether and how irritant controls should be used in patch testing.