Trends and developments in 24 years of patch testing

Background: Allergic contact dermatitis is a common condition with an estimated life prevalence of 19.5%. Patch tests are used to confirm the diagnosis. We reviewed the patch test results of the past 24 years with special regards to legal restrictions on nickel and chromate. Materials & Methods: Retrospective study analyzing the patch test results of the Department Dermatology of the University Medical Center Groningen between January 1989 and December 2012. Patch tests were performed according to the guidelines of the ICDRG and results were read on day 2 and day 3 or on day 3 and day 7. Results: 12,057 consecutive patients were patch tested with the European baseline series. Overall, the three most frequent contact allergens were nickel (18.2%), fragrance mix I (5.6%) and cobalt chloride (4.9%). Over two decades, the prevalence of methylchoroisothiazolinone/ methylisothiazolinone (MCI/MI), nickel sulfate, para-tertiary-butylphenol formaldehyde resin (PTBFR) and paraphenylenediamine (PPD) sensitizations increased, while a significant decrease was observed in sensitizations to colophonium, formaldehyde, fragrance mix I, thiuram mix and quinoline mix. The number of sensitizations to potassium dichromate did not change (3.7%). Discussion: The influence of legal restrictions was not visible in this study. Patients may have been sensitized before legal restrictions were introduced and other sources of exposure should be considered. The increase in sensitizations to MCI/MI is alarming, probably due to the increased exposure to methylisothiazolinone. Conclusion: The patch test results of the standard series are subject to trends and other developments over time, but react slowly to legal restrictions