Marked Impact of Regulatory Bans on Formaldehyde and Formaldehyde‐Releaser‐Induced Allergic Contact Dermatitis: A Retrospective Cohort Study (1996–2024) From Turkey

Abstract

Background: Formaldehyde (FA) and formaldehyde‐releasers (FRs) are well‐known causes of allergic contact dermatitis (ACD). Following the 2019 EU ban on FA and Quaternium‐15 in cosmetics, stable or slightly decreasing sensitisation rates have been reported. In Turkey, both were banned in 2021. Objectives: To assess FA/FR sensitisation and ACD rates before and after the ban, and evaluate the role of FA as a marker for FR allergy. Methods: A single‐centre retrospective cohort of 2592 patients patch tested with FA 1% or 2% aq. and at least one FR between 1996 and 2024. Results: FA/FRs sensitisation prevalence was 1.9% (48/2592), mostly in patients > 40 years old. The most frequent sensitisers were hexahydro‐1,3,5‐tris‐(2‐hydroxyethyl)triazine (0.7%) and Quaternium‐15 (0.6%). ACD occurred in 37.5% (18/48), mainly as hand eczema from non‐occupational rinse‐off cosmetics, while 16.7% were occupational (hairdressers/barbers/metalworkers). FA 1%–2% aq. failed to detect FR sensitisation in 31.9% ( n = 15/47) of patients, including nine missed with FA 1% aq. and six with FA 2% aq. No cases occurred after the 2021 ban. 2‐bromo‐2‐nitropropane‐1,3‐diol and DMDM‐hydantoin showed no co‐reactivity with FA, but were important inducers of FR‐related ACD. Conclusions: The 2021 ban in Turkey appears to have reduced ACD due to FA and FRs. Continued FR testing remains essential, as FA 2% aq. is complementary but not a fully reliable marker.