Memorial for our Editorial Board Member, Kanok Pavusithipaisit

Review Isocyanates, a group of reactive chemicals [with the functional group N = C = O (NCO)] used extensively in the production of numerous polyurethane foams, coatings, and a wide array of consumer products, are a major cause of occupational asthma worldwide. The polyurethane industry has expanded dramatically , along with the number of workers and consumers at risk for exposure. Inhalation has long been considered the primary route of isocyanate exposure, induction of sensitiza-tion, and asthma; research, practice, and regulation have focused almost exclusively on understanding and preventing inhalation exposures. Airborne isocyanate exposures have been reduced through improved controls and use of less-volatile isocyanates. Yet isocyanate asthma continues to occur, not uncommonly in work settings where measured isocyanate respiratory exposures are very low or nondetectable, but where there is opportunity for skin exposure. It has been > 25 years since Karol et al. (1981) demonstrated in guinea pigs that skin contact with isocyanates could lead to sensiti-zation and subsequent asthmatic responses following inhalation exposure. However, knowledge and awareness remain limited regarding the potential for isocyanate skin exposure to contribute to the development of isocyanate asthma. For example, the literature on occupational asthma rarely mentions iso-cyanate skin exposure as a potential risk factor or target for prevention (Nicholson et al. 2005; Tarlo and Liss 2005). Over the past several years there has been a growing, but largely unrecognized, collection of animal, industrial hygiene, clinical, and epidemiologic data related to isocyanate skin exposure and its role in the development of isocyanate sensitization and asthma. Our primary purpose in this article is to review and synthesize this multidisciplinary literature to address several key unresolved issues, including the extent of isocyanate skin exposures in the workplace, the effectiveness of personal protective equipment , and most importantly, whether human skin exposure contributes to the development of isocyanate asthma. The findings may be relevant to the larger issue of the role of skin as an important underrecognized site of exposure and sensitization for other environmental allergens. Methods Definition of terms. The terms " skin exposure " and " dermal exposure " are used interchangeably to indicate exposure to the outermost layer of the epidermis or epicutaneous exposure , as is commonly done in the occupational and environmental literature. " Isocyanates " refers to diisocyanate monomers (two NCO groups) and their related polyisocyanates, which have similar health effects (Bello et al. 2004). The term " sensitization …