appears shortly after exposure and, although refractory to treatment, usually regresses over time and does not appear after a long latency. New cases of chloracne are therefore not a concern of this report.

Chloracne is a highly characteristic form of acne. It shares some pathological processes, such as occlusion of the orifice of the sebaceous follicle, with much more common forms of acne such as acne vulgaris. However, it is marked by a unique feature, the epidermoid inclusion cyst, which is caused by proliferation and hyperkeratinization (horn-like cornification) of the epidermis. Although typically appearing in a characteristic distribution over the eyes, ears, and neck, patterns of chloracne among exposed chemical industry workers may involve 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, as such residents involved in the 1976 industrial incident in Seveso, Italy, and to 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 these compounds, particularly TCDD (Sweeney et al., 1997/ 98). The predictive value of chloracne as a biomarker is suggested by its strong association with other health outcomes, such as goiter, arthritis, and anemia in the Taiwanese population affected by the “Yucheng” (cooking oil disease) incident in 1979, in which there was exposure to high levels of PCBs (Guo et al., 1999).

Despite the utility of chloracne as a biomarker, and the general association with high blood levels of TCDD and related compounds, it has not been possible to identify a threshold level for the skin condition. Kimbrough (1998) suggests that this may be because blood levels do not necessarily reflect levels in skin. She also suggests that susceptibility due to different skin conditions may obscure the association or that direct dermal deposition may play a greater role in some situations. Kimbrough suggests that Ranch Hand veterans have too narrow and too low a range of blood levels from which to draw conclusions and also that the time elapsed after exposure until the studies were performed may have introduced confounding factors such as aging, obesity, and onset of diabetes, all of which change blood lipid levels in ways that may not affect skin changes and that may obscure relationships with chloracne.

One new study to shed light on the elusive threshold for development of chloracne was contributed by Coenraads et al. (1999), reporting on four groups of Chinese workers involved in industrial incidents that exposed them to polycyclic organochlorines, particularly TCDD. They reported their findings in terms of 2,3,7,8-TCDD toxicity equivalents (TEQs) in pooled blood, levels of exposure to these compounds weighted by their TCDD-like activity. They inferred a threshold for chloracne (per gram of blood lipid) between 650 and 1,200 pg/g TEQ. They also suggested that in this population, the contribution to the risk of developing chloracne from exposure to TCDD itself was small compared to the hexachlorinated dibenzodioxins and furans, a finding that may be specific to this population and the exposure conditions.

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