Background Methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) contact dermatitis is a severe problem. The high concentrations of these substances and other isothiazolinones such as benzisothiazolinone (BIT) and octylisothiazolinone (OIT) contained in cleaning products may cause allergic contact dermatitis in sensitized patients. Objectives To evaluate the exposure to isothiazolinones contained in cleaning products on the market and from sensitized patients, and to verify the accuracy of labeling. Methods A total of 34 cleaning products were collected (17 supplied by sensitized patients and 17 bought randomly). Analysis was made of the concentrations of MI, MCI, BIT, and OIT using liquid chromatography tandem mass spectrometry (LC‐MS/MS). Results MI and BIT were the components most frequently detected. Of all the products analyzed, 76.5% contained at least one isothiazolinone. Twelve products had an MI concentration above the permitted level for rinse‐off cosmetics. Most of them were coming into direct contact with the skin in daily use. Mislabeling occurred in eight products. Conclusions Some cleaning products with high concentrations of isothiazolinones may cause cutaneous symptoms in sensitized patients, especially in spray form. The labeling should be correct, also regarding the use of each article.

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BackgroundSensitization to methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) is a worldwide problem. Washing machine detergents are suspected to cause cutaneous symptoms in highly sensitized patients. Little is known about the persistence of isothiazolinones in clothes that have been washed.ObjectiveThe aim of the study was to analyze the possible persistence of MI, MCI, benzisothiazolinone, and octylisothiazolinone in common fabrics after machine washing.MethodsDifferent clothes (cotton, polyester, linen, and wool) were collected, and 4 types of wash were done (control, standard, standard + conditioner, and standard + double rinse). The samples were analyzed using ultrahigh-performance liquid chromatography.ResultsThe results showed that the concentrations of isothiazolinones were very low, independent of the type of material or wash. The highest levels were found in the control wash (hand wash), reaching a maximum of 0.4 ppm in the linen.ConclusionsOur findings suggest that it is not necessary to recommend that patients sensitized to MI avoid isothiazolinones in machine detergents or fabric conditioners or to double rinse. However, after using the detergent for hand washing (the control in our study), there may remain sufficient concentrations of isothiazolinones in clothes to produce symptoms in highly sensitized patients.