Chloracne is a skin disease that is characteristic of exposure to TCDD and other diaromatic organochlorine compounds. It shares some pathologic processes (such as the occlusion of the orifice of the sebaceous follicle) with more common forms of acne (such as acne vulgaris), but it can be differentiated by the presence of epidermoid inclusion cysts, which are caused by proliferation and hyperkeratinization (horn-like cornification) of the epidermis and sebaceous gland epithelium. Although chloracne is typically distributed over the eyes, ears, and neck, among chemical-industry workers exposed to TCDD it can also occur on the trunk, genitalia, and buttocks (Neuberger et al., 1998).
Chloracne has been exploited as a marker of exposure in epidemiologic studies of populations exposed to TCDD and related chemicals. It is one of the few findings in humans that are consistently associated with such exposure, and it is a well-validated indicator of high-dose exposure to TCDD and related compounds (Sweeney et al., 1997/1998). If chloracne occurs, it appears shortly after the chemical exposure, not after a long latent period. Although it is resistant to acne treatments, it usually regresses over time. Therefore, new cases of chloracne in Vietnam veterans would not be the result of exposure during Vietnam and are not of concern for this report. It should be noted that absence of chloracne does not necessarily indicate absence of substantial exposure to TCDD, as is apparent from studies of people with documented exposure to TCDD after the Seveso accident (Baccarelli et al., 2005a). And there is not necessarily a correlation between serum TCDD concentrations and the occurrence or severity of chloracne.
The committee responsible for Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam, hereafter referred to as VAO (IOM, 1994), determined that there was sufficient evidence of an association between exposure to at least one compound of interest and chloracne. Additional information available to the committees responsible for Veterans and Agent Orange: Update 1996 (IOM, 1996), Update 1998 (IOM, 1999), Update 2000 (IOM, 2001), Update 2002 (IOM, 2003), and Update 2004 (IOM, 2005) did not change that conclusion. Reviews of the studies that underlie the conclusion can be found in the earlier reports.
Since Update 2004, there has been a single environmental study concerning chloracne and a publication of case reports, one of which involved a high-profile news story.