Chloracne in the mouse. (A) Skin from a control male B6C3F1 mouse in the 2-year NTP study for 3,3',4,4'-tetrachloroazobenzene (TCAB). Hair follicles are normal, and adjacent sebaceous glands can be seen. Black arrows indicate hair follicles; open arrows indicate sebaceous glands. (B) Skin from a male B6C3F1 mouse treated for 2 years with TCAB (30 mg/kg). Note dilation of hair follicles, flattening of the epithelial lining, and atrophy of adjacent sebaceous glands. No infiltration of inflammatory cells can be discerned. This animal was assigned a moderate degree of hair follicle dilation (i.e., six or more follicles segmentally dilated to greater than double the normal diameter within a low-magnification field). Black arrows indicate dilated hair follicles; open arrows indicate atrophic sebaceous glands. (Reprinted from Ramot et al. [2009], with permission from Elsevier.) H&E.