A decade of trends in patch test allergen sensitisation from a dermatology centre in Southeast Asia

Background Geographical and socioeconomic factors influence the type of allergens causing allergic contact dermatitis. Aim To investigate the changing trends of allergen sensitisation among patch-tested patients. Methods A retrospective study was performed on patients undergoing patch testing (PT) over 11 years (2012-2022). Data were retrieved from medical records. Results A total of 1035 patients were identified; 59 cases were excluded for incomplete data/wrong indication. Median age was 37 years (IQR 26-57) with bimodal peaks at 25-40 and 55-65 years; 69% were females. History of atopy was present in 76.5% patients. Common dermatitis sites were hands 436 (47.0%), feet 303 (32.7%), and head/ neck region 294 (31.7%). PT positivity rate was 885(89%). Top sensitising allergens were methyldibromoglutaronitrile (MDBGN), formaldehyde, potassium dichromate, nickel sulphate, and fragrance mix. In the cosmetic series, the main allergens were propylene glycol, thimerosal, and tert-butylhydroquinone. MDBGN showed an increasing trend, becoming the leading allergen from 2015-2020 before declining. Formaldehyde sensitisation rose until 2017, then stabilised. Potassium dichromate remained stable with peaks in 2015 and 2018. Cosmetic allergen sensitisation declined during the COVID-19 pandemic, likely due to reduced exposure. Limitations This single-centre study lacked extended PT readings beyond day 4, did not assess clinical relevance, and reflects sensitisation rather than confirmed allergic reactions. Conclusions Preservatives such as MDBGN, formaldehyde, and thimerosal were major sensitisers, alongside potassium dichromate, nickel, fragrance mix, and propylene glycol. Longitudinal analysis of allergen trends aids clinical management, guides PT updates, and directs regulatory decisions.