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. Sensitization to methylisothiazolinone (MI), methylchloroisothiazolinone (MCI)/MI and benzisothiazolinone (BIT) is still common in Spain, while sensitization to octylisothiazolinone is rare. Sensitization to MI and MCI/MI is probably work‐related, and linked to hand dermatitis, detergents and age over 40. Origin of sensitization to BIT is unknown, although linked to higher ages.