Positive Patch Test Reactions to Carba Mix and Iodopropynyl Butylcarbamate

Abstract

Carba mix (CM) contains 3 chemicals used as accelerators in manufacturing of rubber products and agricultural chemicals. Iodopropynyl butylcarbamate (IPBC) is a preservative used in industrial and personal care products. Potential cross-reactivity between these allergens is unclear. This study aimed to determine concomitant reaction rates between CM (3% petrolatum [pet]) and IPBC (0.1% pet and/or 0.5% pet). A retrospective cross-sectional analysis of data from the North American Contact Dermatitis Group from 1998 to 2008 was conducted. Frequencies of positive reactions, strength of reactions, and concomitant reaction rates were calculated. A total of 25,435 patients were tested. There were 1131 allergic reactions to CM and 346 positive reactions to IPBC (either 0.1% pet and/or 0.5% pet). Fifty-two patients reacted to both allergens. Most reactions (>69%) were doubtful/weakly positive, and of those who reacted to both, most (58%) had doubtful and/or weakly positive reactions. There was a statistically significant association of concomitant reactions between CM and IPBC; formaldehyde positivity was used as control and showed statistically significant concomitant reactions. Overall, concomitant reactions to CM and IPBC were low, and rates varied by strength of reaction. True cross-reactivity is unlikely; statistical association is likely due to frequent low-grade reactions to irritant patch test preparations.