Sensitization to isothiazolinones in the Spanish Contact Dermatitis Registry (REIDAC): 2019–2021 epidemiological situation

Background: Current frequency and risk factors for sensitization to methylisothiazolinone (MI), methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), benzisothiazolinone (BIT) and octylisothiazolinone (OIT) in Spain are not well known. Objectives: To study the frequency of sensitization, risk factors and simultaneous sensitization between the four isothiazolinones. Materials and Methods: We analysed all 2019-2021 consecutive patients patch-tested with MI (0.2% aq.), MCI/MI (0.02% aq.), BIT (0.1% pet.) and OIT (0.1% pet) within the Spanish Contact Dermatitis Registry (REIDAC). Results: A total of 2511 patients were analysed. Frequencies of sensitization were: any isothiazolinone 15.7%, MI 6.8%, MCI/MI 4.8%, BIT 3.5% and OIT 0.5%. MI and MCI/MI sensitization was associated with being occupationally active, hand dermatitis, detergents and age over 40. BIT sensitization was associated with leg dermatitis and age over 40. About one in nine MI-positive patients were positive to BIT, whereas one in five BIT-positive patients were positive to MI. Conclusions: Sensitization to MI, MCI/MI and BIT is still common in Spain, while sensitization to OIT is rare. Currently, sensitization to MI and MCI/MI seems to be occupationally related. Although its origin is unknown, sensitization to BIT is more frequent in patients aged over 40 years. Simultaneous sensitization between MI and BIT is uncommon.The Spanish Registry of Contact Dermatitis (REIDAC) is promoted by the Fundación Piel Sana (Academia Española de Dermatología y Venereología), which has received financial support from the Spanish Medicines and Health Products Agency (Agencia Española de Medicamentos y Productos Sanitarios. https://www.boe.es/boe/dias/2022/04/11/pdfs/BOE-A-2022-5975.pdf) and Sanofi. The funders were not involved in the design and conduct of the study, collection, management, analysis and interpretation of data, preparation, review, approval of the manuscript, or decision to submit the manuscript for publication