Occupational allergic contact dermatitis from 2-N-octyl-4-isothiazolin-3-one

2-N-octyl-4-isothiazolin-3-one (OIT) is an antimicrobial agent that is mainly used in industrial settings. The objective of the study was to find the significance of OIT contact allergy at our clinic of occupational dermatology. We looked through our patient material from 1991 for allergic reactions to OIT and analysed the clinical records. We found 8 patients with ordinary allergic reactions to OIT and 1 late reaction. 2 workers in the manufacture of paints had occupational allergic contact dermatitis from OIT in biocides. 2 patients were machinists and 3 were female farmers: in these cases, however, we could not find any exposure. A sewing machine operator had patch test reactions to 2 of her mattress textiles, and chemical analysis of them showed 40-50 parts per million OIT. In conclusion, OIT is a rare sensitizer, and its contact allergies occur mainly in paint manufacturing. It is infrequently used in metal-working fluids and possibly sensitizes machinists. Although it is also used in some biocides recommended for use in the textile industry, there are no previous reports of contact allergy in this field. Our sewing machine operator with OIT contact allergy had probably been sensitized from mattress textiles.