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Positive Patch Test Reactions to Carba Mix and Iodopropynyl Butylcarbamate: Data From the North American Contact Dermatitis Group, 1998–2008

Warshaw, Erin M. MD, MS*; Raju, Srihari MD*; DeKoven, Joel G. MD; Belsito, Donald V. MD; Zug, Kathryn A. MD§; Zirwas, Matthew J. MD; Maibach, Howard I. MD; Taylor, James S. MD#; Sasseville, Denis MD**; Fowler, Joseph F. Jr MD††; Mathias, C.G. Toby MD‡‡; Fransway, Anthony F. MD§§; DeLeo, Vincent A. MD; Marks, James G. Jr MD∥∥; Pratt, Melanie D. MD¶¶; Storrs, Frances J. MD##

doi: 10.1097/DER.0b013e3182a5a1d4

Background 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.

Objective This study aimed to determine concomitant reaction rates between CM (3% petrolatum [pet]) and IPBC (0.1% pet and/or 0.5% pet).

Design 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.

Results 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.

Conclusions 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.

From the *Department of Dermatology, Veterans Affairs Medical Center, University of Minnesota, Minneapolis, MN; †Division of Dermatology, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada; ‡Department of Dermatology, Columbia University, New York, NY; §Dartmouth-Hitchcock Medical Center, Lebanon, NH; ∥Ohio State University Medical Center, Columbus, OH; ¶Department of Dermatology, University of California San Francisco, San Francisco, CA; #Department of Dermatology, Cleveland Clinic, Cleveland, OH; **Division of Dermatology, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada; ††Department of Dermatology, University of Louisville, Louisville, KY; ‡‡Department of Dermatology, University of Cincinnati, Cincinnati, OH; §§Private practice, Fort Myers, FL; ∥∥Department of Dermatology, Pennsylvania State University, Philadelphia, PA; ¶¶Division of Dermatology, University of Ottawa, Ottawa, Ontario, Canada; and ##Department of Dermatology, Oregon Health Science University, Portland, OR.

Address correspondence to Erin M. Warshaw, MD, MS, Section of Dermatology, Minneapolis Veterans Affairs Medical Center, University of Minnesota Medical School, 1 Veterans Dr, 111K-Dermatology, Minneapolis, MN 55417. E-mail:

The authors declare no conflicts of interest.

Disclaimer: This material is the result of work supported with resources and the use of facilities at the Minneapolis Veterans Affairs Medical Center in the United States. The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of the Department of Veterans Affairs or the United States government.

© 2013 American Contact Dermatitis Society
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