Methyldibromoglutaronitrile in rinse-off products causes allergic contact dermatitis: an experimental study

BACKGROUND: The frequency of sensitivity to the cosmetic preservative methyldibromoglutaronitrile (MDBGN) has increased significantly in Europe. Most cases of allergic contact dermatitis from MDBGN are caused by leave-on cosmetic products. The risk of developing allergic contact dermatitis from rinse-off products has been less studied.

OBJECTIVES: To investigate the allergic response elicited in presensitized individuals from exposure to a rinse-off product preserved with the maximum permitted level of MDBGN.

METHODS: Nineteen contact allergic individuals and nine controls participated in a double-blind, randomized repeated open application test (ROAT) using two coded liquid soaps with and without MDBGN. Areas of 50 cm2 on the lower arms were washed with the soaps twice a day for up to 28 days; two of the subjects continued for 34 days. The subjects were also patch tested with a dilution series of MDBGN to determine their patch test threshold values.

RESULTS: Seven presensitized individuals (37%) developed allergic contact dermatitis from the soap containing MDBGN. The mean dose of MDBGN per application was 2.2 micro g cm-2 and the reactions appeared between days 6 and 34. All nine controls had negative ROATs. The difference in reactivity between test subjects and controls was significant (one-sided Fisher's exact test, P = 0.04). Patch test threshold values ranged from < 0.001% to 0.2% MDBGN in ethanol/water.

CONCLUSIONS: This study shows that the exposure to a rinse-off product containing the maximum permitted level of MDBGN can easily elicit an allergic response in presensitized individuals. Along with reported cases of induction and elicitation caused by MDBGN in rinse-off products the study indicates that the permitted level of MDBGN in rinse-off products is too high. We recommend that this level should be re-evaluated.