Temporal trends of preservative allergy in Denmark (1985-2008)

Low-level efficacy of cosmetic preservatives

Preservation using combinations of preservatives has several advantages. This study shows that the concentration of some of the most frequently used allergenic preservatives can be markedly lowered when they are combined with phenoxyethanol. The antimicrobial efficacy of cosmetic preservatives and known allergens of various potency [diazolidinyl urea, methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), methylisothiazolinone (MI) and phenoxyethanol] was tested alone and in various combinations of two or three preservatives together. The preservatives were tested for minimum inhibitory concentration (MIC) values and possible synergy using fractional inhibitory concentration. MCI/MI was the only preservative showing low-level MIC against all four tested microorganisms: Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger. Different combinations of the preservatives indicated additive effects against the microorganisms. No combination of preservatives showed any inhibitory action on each other. Challenge tests with different concentrations and combinations were performed in a cosmetic cream. Diazolidinyl urea and MCI/MI alone were ineffective against C. albicans in a challenge test at concentrations up to 16 times higher than the observed MIC values. When combining phenoxyethanol with either one of the allergenic preservatives diazolidinyl urea, MCI/MI or MI, the cosmetic cream was adequately preserved at concentrations well below the preservatives' MIC values as well as 10-20 times below the maximum permitted concentrations. By using combinations of preservatives, effective preservation can be achieved with lower concentrations of allergenic preservatives.

Characteristics of patch test reactions to common preservatives incorporated in petrolatum and water, respectively

BACKGROUND

The irritant properties of some preservatives and the use of water as the patch test vehicle for some of them call for a critical evaluation of patch test reactions to preservatives.

OBJECTIVES

To examine the association between test vehicle (petrolatum versus water) or the patients' age and history of atopic dermatitis, respectively, and certain patterns of reaction to preservatives.

PATIENTS/METHODS

Data of 34,631 patients tested in 34 centres with 11 common preservatives were retrospectively analysed. The dynamic reaction patterns, reaction indices (RIs) and positivity ratios (PRs) were statistically evaluated.

RESULTS

All preservatives yielded more crescendo reactions in older than in younger patients. For 10 of 11 preservatives, the percentage of crescendo reactions was slightly higher in patients without a history of atopic dermatitis, and for 10 of 11 agents the RI was higher in patients with a positive history of atopic dermatitis. No consistent vehicle-related effects on reaction characteristics were found. Chlorhexidine digluconate 0.5% in water and sodium benzoate 5% in petrolatum had the lowest RIs, highest PRs, and lowest proportions of crescendo reactions.

CONCLUSIONS

Water as a vehicle is unlikely to affect the reaction patterns of preservatives. The generally used patch test preparations of chlorhexidine digluconate and sodium benzoate need improvement.