AbstractBackgroundMethylchloroisothiazolinone/methylisothiazolinone (MCI/MI) and MI allergy caused a global epidemic during the period 2010 to 2015, reaching its peak in 2013/14.ObjectiveTo investigate the characteristics of MCI/MI and MI allergy in Turkey over 24 years.MethodsA total of 2310 patients patch tested between 1996 and 2019 with MCI/MI 0.01% aq. or MCI/MI 0.02% aq., with or without MI 0.2% aq., were analyzed.ResultsThe overall prevalence of contact sensitization was 3.3% (n = 77) with a peak level of 16.4% in 2015. The prevalence gradually decreased thereafter, but was still high (6.5%) in 2019. Seventy‐three patients had clinically relevant sensitizations. MI could detect clinically relevant sensitizations in all seven patients with a negative patch test reaction to MCI/MI 0.02%. Non‐occupational allergic contact dermatitis (ACD) was most frequently seen, mainly in women, with hand/face eczema from rinse‐off or leave‐on cosmetics, such as wet wipes. Occupational ACD was mainly seen among men with airborne eczema from wall paints in house painters, or with hand eczema from hair gel/wax in men's barbers.ConclusionsThe prevalence of MCI/MI and MI sensitization in Turkey following the peak in 2015 is still high. This is probably due to the currently allowed level of 100 ppm for MI in rinse‐off cosmetics. This needs to be urgently reduced.