of epidermoid inclusion cysts, which are caused by proliferation and hyperkeratinization (horn-like cornification) of the epidermis. Although chloracne is typically distributed over the eyes, ears, and neck, patterns of chloracne among chemical-industry workers exposed to TCDD have also included the trunk, genitalia, and buttocks (Neuberger et al., 1998).

Chloracne has been extensively studied and is used as a marker of exposure in studies of populations exposed to TCDD and other organochlorine compounds, such as polychlorinated biphenyls (PCBs) and pentachlorophenol. It is one of the few findings consistently associated with such exposure and is a well-validated indicator of high exposure to those compounds, particularly TCDD (Sweeney et al., 1997/98). If chloracne occurs, however, it appears shortly after the chemical exposure, not after a long latency. Although it is refractory to acne treatments, it usually regresses over time. Therefore, new cases of chloracne would not be the result of exposures during Vietnam and are not a concern for this report.

Summary of VAO, Update 1996, Update 1998, and Update 2000

The committee responsible for Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam (hereafter referred to as VAO; IOM, 1994) found there to be sufficient information of an association between exposure to at least one of the chemicals of interest (2,4-D, 2,4,5-T or its contaminant TCDD, picloram, or cacodylic acid) and chloracne. Additional information available to the committees responsible for Veterans and Agent Orange: Update 1996 (IOM, 1996), Update 1998 (IOM, 1999), and Update 2000 (IOM, 2001) did not change that finding. Reviews of the studies underlying the finding may be found in the earlier reports.

Update of the Scientific Literature

No relevant occupational, environmental, or Vietnam-veteran studies have been published since Update 2000 (IOM, 2001).

Synthesis

Chloracne is clearly associated with high exposure to cyclic organochlorine compounds, but it appears shortly after exposure, not after a long latency.

Conclusions
Strength of Evidence from Epidemiologic Studies

On the basis of its evaluation of the epidemiologic evidence reviewed in this and previous Veterans and Agent Orange reports, the committee finds that there



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