Background: For more than 30 years, fragrance mix I (FMI) has been the most important screening marker for fragrance contact allergy. Meanwhile, governmental and corporate initiatives have been implemented, aimed at reducing sensitization to fragrance allergens, including the single constituents of FMI. Objectives: To examine trends in contact allergy to FMI from 1986 to 2015 in patients with dermatitis, and to test the hypothesis that sensitization to the fragrance screening marker has decreased within recent years. Methods: This was a cross-sectional registry study on patch test results to FMI among consecutively tested patients with dermatitis from a single university clinic across three 10-year periods. From 2006 to 2015, data on eczema location according to the MOAHLFA index (male; occupation; atopic dermatitis; hand; leg; face; age ≥ 40 years), clinical relevance of sensitization, and cosmetic exposures were available. Results: Of 24 168 patients, 7·8% (95% confidence interval 7·4–8·1) were sensitized to FMI. For women, a significant trend (P = 0·004) was observed for an increase in sensitization to FMI across the three decades. From 2011 to 2015, the prevalence of contact allergy to FMI increased significantly for women (8·0% vs. 10·4%, P = 0·002) and men (4·4% vs. 7·3%, P = 0·002) compared with the previous 5-year period. From 2006 to 2015, clinical relevance was established in 78·2% of FMI-positive patients with no differences over time. An increase (28·6% vs. 36·1%, P = 0·05) in FMI-positive patients suffering from facial dermatitis was observed for the period 2011 to 2015 compared with 2006 to 2010. Conclusions: The prevalence of contact allergy to FMI has been increasing in recent years. There was no demonstrable effect of previous preventive initiatives.