Contact Dermatitis

Methylisothiazolinone and Isothiazolinone Allergy

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Other Isothiazolinones

Other isothiazolinones also are known to cause ACD, albeit less commonly than MI. Benzisothiazolinone has been identified in glues, cleaning agents, paints, and industrial chemicals; unlike MI, the presence of BIT is infrequent in personal care products.15,29 This chemical is not commonly included in patch test screening series in the United States but is currently present in the NACDG screening series as BIT 0.1% in petrolatum.

Octylisothiazolinone (OIT) has been reported in leather furniture, belts, shoes, and watchbands, as well as industrial chemicals.30,31 Similar to BIT, OIT is not commonly tested in screening series in the United States; the NACDG tests this chemical as OIT 0.025% in petrolatum.

The cross-reaction patterns between the isothiazolinones remain uncertain. A study in mice supported cross-reactivity between MI, OIT, and BIT32; however, several clinical epidemiologic studies suggested that although there is evidence that there may be cross-reactivity between OIT and MI, concomitant positive BIT and MI reactions more likely represent cosensitization.33-35

Final Interpretation

Methylisothiazolinone continues to have high positive patch test rates in North American patch test populations and should be tested at a concentration of 2000 ppm (0.2% aqueous). Methylisothiazolinone may now be rare in wet wipes, but it is still present in numerous personal care products including hair care products, liquid soaps, and cleaning products. Novel exposures to MI include paint, slime, and glues. It also is important to remember that MI can cause photoaggravated or photoallergic contact dermatitis and might be a worthy addition to photopatch test trays. Finally, keep a look out for BIT and OIT, which may be present in industrial chemicals, glues, paints, cleaning products, and leather items.


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