SummaryBackgroundIn recent years, the frequency of contact allergy to isothiazolinones has increased alarmingly in Europe, but only limited data are available on concentrations of isothiazolinones in consumer products.ObjectivesTo examine the current frequency of isothiazolinones [methylisothiazolinone (MI), methylchloroisothiazolinone (MCI), benzisothiazolinone (BIT), and octylisothiazolinone (OIT)] in a wide array of detergents and cosmetics relevant for the Swiss population.MethodsBy means of a market survey, the occurrence of isothiazolinones was investigated in 1948 consumer products. Of these, 88 products were analysed by liquid chromatography–high‐resolution mass spectrometry after ultrasonic extraction.ResultsOnly 7.6% of all cosmetics contained isothiazolinones, but the prevalence in detergents was much higher (42.9%). The measured concentration ranges in detergents were 4.3–10, 3.5–279, 3.8–186 and 7.9 ppm (one product only) for MI, MCI, BIT, and OIT, respectively. For cosmetics, these were 1.3–133 and 4.8 ppm (one product only) for MI and MCI, respectively.ConclusionsOur study has shown that high concentrations of isothiazolinones (including MI) can be found in a large variety of products, in particular in detergents. Therefore, the safe use of these preservatives should be re‐evaluated by including detergents in the exposure assessment.