Chapter 19: Toxic Responses of the Skin

Introduction

As the body's first line of defense against external insult, the skin's enormous surface area (1.5-2 m²) is exposed routinely to chemicals and may inadvertently serve as a portal of entry for topical contactants. Recognizing the potential hazards of skin exposure, the National Institute of Occupational Safety and Health (NIOSH) characterized skin disease as one of the most pervasive occupational health problems in the United States. In 1982, NIOSH placed skin disease in the top 10 leading work-related diseases based on frequency, severity, and the potential for prevention. Data from the Bureau of Labor Statistics indicate that in 2004 skin disease attributed to workplace exposures accounted for nearly 16% of reported nonfatal occupational disease in private industry; incidence data indicate a rate of 4.4 cases per 10,000 or nearly 39,000 new cases per year. On that basis, the annual economic burden of dermatitis in workers in the USA has been estimated as ≈$1.2 billion (Blanciforti, 2010). Substantial reduction in the reported incidence has occurred in recent years thanks to workplace cleanup and better personal protective equipment. Nevertheless, improvements in prevention and management are needed for continued progress (Emmett, 2003). Skin conditions resulting from exposures to consumer products or occupational illnesses not resulting in lost work time are poorly recorded and tracked. Hence, the incidence of such skin diseases appears greatly underestimated.

NIOSH recently changed its skin notations to reflect more accurately the varied risks to workers after topical exposure (see DHHS(NIOSH) Publication No. 2009-147, www.cdc.gov/niosh). Previously, inhalation exposures were thought to produce the most risk to workers, with skin exposure being only a secondary exposure pathway. The new guidelines now reflect increased understanding of several pathways by which skin exposure can lead to disease: systemic toxicity via skin absorption (SYS), direct effects that damage the skin (DIR), and immune-mediated responses to chemicals that contact the skin (SEN). The new notations utilize these categories to designate hazard-specific skin notations, and have incorporated standard criteria to ensure consistency in how chemicals are designated. Determining the hazard potential of a particular chemical is based on physicochemical properties of the substance, toxicokinetic studies, epidemiological data, in vitro or in vivo laboratory testing, and in silico computational predictions. These criteria are specified in the chemical designation.

Skin as a Barrier

A large and highly accessible human organ, the skin protects the body against external insults to maintain internal homeostasis. Its biological sophistication allows it to perform a myriad of functions above and beyond that of a suit of armor. Physiologically, ...