Background: Preservatives are well-known and important contact allergens.

Objectives: To examine the frequency of sensitization to preservatives, including time trends.

Methods: Retrospective analysis of data on patch testing of preservatives contained in the standard series and special series collected by the IVDK (Informationsverbund Dermatologischer Kliniken) during 1996-2009.

Results: Some 120,000 and 80,000 patients were tested with the baseline and the preservative series, respectively.  Sensitization frequencies of the standard series allergens all ranged above 1%: methyldibromoglutaronitrile (MDBGN) 2.36-4.5%, methyl(chloro)isothiazolinone (MCI/MI) 2.22%, formaldehyde 1.54%, paraben mix 1.33% and Bronopol (R) 1.25%.  Regarding the special preservative series, 1.54% reacted positive to methylisothiazolinone (MI), and less than 1% to the other preservatives.  Concomitant reactions to formaldehyde in formaldehyde releasers ranged from 15% to almost 50%, and 67% of MI positives reacted to MCI/MI.  As indicated by the MOAHLFA index, sensitization to MI, iodopropynylbutyl carbamate (IPBC) and quaternium 15 was associated more often with occupational dermatitis, whereas sensitisation to imidazolidinyl urea and diazolidinyl urea was associated with face dermatitis, indicating cosmetic exposure.  Epidemiologically relevant decreases (more than 10%) were seen in chloroacetamide, benzyl alcohol and MDBGN.  Epidemiologically relevant increases were noted in IPBC, sodium benzoate and MI.

Conclusions: Preservatives are still important contact allergens.  The introduction of new preservatives should consider the specific characteristics of occupational and of nonoccupational (cosmetic, household) exposure, and preventive measures should aim equally at both areas.