BACKGROUND: In recent years, the prevalence of contact allergy to isothiazolinones has reached epidemic levels. Few studies have presented data on occupations at risk of developing contact allergy to isothiazolinones.

OBJECTIVES: To present demographics and examine risk factors for sensitization to methylisothiazolinone (MI), methylchloroisothiazolinone (MCI) in combination with MI and benzisothiazolinone (BIT) in Danish dermatitis patients.

MATERIALS AND METHODS: A retrospective epidemiological analysis of data from three Danish hospitals departments was conducted. All patients consecutively patch tested with MI, MCI/MI and BIT between 2009 and 2013 were included.

RESULTS: MI contact allergy showed a significantly increased trend in prevalence from 1.8% in 2009 to 4.2% in 2012 (p < 0.001). Females with facial dermatitis mainly drove the increase in 2012. Adjusted logistic regression analysis showed that MI sensitization was significantly associated with occupational exposures, hand and facial dermatitis, age > 40 years, and the occupational groups of tile setters/terrazzo workers, machine operators, and painters. MCI/MI contact allergy was significantly associated with the following high-risk occupations: painting, welding (blacksmiths), machine operating, and cosmetology. The occupational group of painting was frequent in the group of patients with BIT contact allergy.

CONCLUSION: Several high-risk occupations for sensitization to isothiazolinones exist. Regulation on the allowed concentration of isothiazolinones, and especially MI, in both consumer products and industrial products is needed.