Patch Testing With a New Composition of the Mercapto Mix-A Multicenter Study from the International Contact Dermatitis Research Group.

Background: Mercaptobenzothiazole compounds are associated with allergic contact dermatitis caused by rubber products. Several screening substances have been used for patch testing.

Objective: To compare the frequency of positive test reactions to a mercapto mix containing a higher concentration of 2-mercaptobenzothiazole with reactions to the combination of 2-mercaptobenzothiazole 2.0% and mercapto mix 2.0%.

Methods: There were 7103 dermatitis patients in 12 International Contact Dermatitis Research Group dermatology departments who were patch tested with 2-mercaptobenzothiazole 2.0% petrolatum (pet.), mercapto mix 2.0% pet., and mercapto mix 3.5% pet.

Results: Contact allergy to the 3 test preparations varied among the 12 centers: 2-mercaptobenzothiazole 2.0% pet. (0-2.4%), mercapto mix 2.0% pet. (0-4.9%), and mercapto mix 3.5% pet. (0-1.4%). 2-Mercaptobenzothiazole 2.0% and mercapto mix 2.0% detected a few more positive patients compared with mercapto mix 3.5%, but the difference was statistically insignificant (mercapto mix 2.0% pet., P = 1.0; 2-mercapto-benzothiazole 2.0% pet., P = 0.66).

Conclusions: Mercapto mix 3.5% pet. is not better than 2-mercaptobenzothiazole 2.0% and mercapto mix 2.0% by a difference that is significant. By using only 1 test preparation (mercapto mix 3.5%), an additional hapten could be tested. No cases of suspected/proven patch test sensitization were registered.