Isothiazolinone (/ˌaɪsoʊˌθaɪ.əˈzoʊlɪnoʊn/; sometimes isothiazolone) is an organic compound with the formula (CH)2SN(H)CO. A white solid, it is structurally related to isothiazole.

[7] DCOI has been detected in both port water and sediment samples in Osaka, Japan, especially in weakly circulating mooring areas.

[10] In 2014 the European Commission Scientific Committee on Consumer Safety reported: "The dramatic rise in the rates of reported cases of contact allergy to MI, as detected by diagnostic patch tests, is unprecedented in Europe; there have been repeated warnings about the rise (Gonçalo M, Goossens A.

"[11] In 2014, the European Commission Scientific Committee on Consumer Safety further issued a voluntary ban on "the mixture of Methylchloroisothiazolinone (and) Methylisothiazolinone (MCI/MI) from leave-on products such as body creams.

[13] Additionally, new research into cross reactivity of MI-sensitized patients to variants benzisothiazolinone and octylisothiazolinone have found that reactions may occur if present in sufficient amounts.

[14] Methylisothiazolinone is used commonly in products in conjunction with methylchloroisothiazolinone, a mixture sold under the registered trade name Kathon CG.

The committee concluded: “Current clinical data indicate that 100 ppm MI in cosmetic products is not safe for the consumer.

"For leave-on cosmetic products (including ‘wet wipes’), no safe concentrations of MI for induction of contact allergy or elicitation have been adequately demonstrated.

"For rinse-off cosmetic products, a concentration of 15 ppm (0.0015%) MI is considered safe for the consumer from the view of induction of contact allergy.

However, no information is available on elicitation.”[20] Colgate-Palmolive had added it as an ingredient in a mouthwash put onto the market in August 2014 with the name Colgate Total Lasting White.