The irritancy and allergenicity of 2-n-octyl-4-isothiazolin-3-one (Skane M-8), with recommendations for patch test concentration.

Preparations of 2-n-octyl-4-isothiazolin-3-one (Skane M-8) at 1000 p.p.m. a.i. and 500 p.p.m. a.i. in pet. induced allergy in a cumulative insult human patch test. Challenge patch testing using 250 p.p.m. a.i. Skane M-8 elicited allergy in 6 out of 6 sensitized individuals. Sensitized individuals did not cross react with Kathon biocide, (Kathon CG), a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one. All pretrolatum preparations to which Tween 85 was added at 2.5% produced mild irritation in cumulative insult patch tests, but no irritation was observed with Tween 85 at 0.625%. We conclude that Skane M-8, 250 p.p.m. a.i. with Tween 85 0.625% in petrolatum is appropriate for patch testing for Skane M-8 allergy.