Histopathological examination
The paraffin-fixed skin samples were sectioned and stained using hematoxylin-eosin for pathological examination. Histopathological anomalies, such as hyperplasia of the epidermis, hyperkeratosis, inflammatory infiltrates, or epidermal degeneration, were recorded and scored using a numerical scale. The gross and histological scores of the lesion samples from Changan and Ningshan were analyzed using the independent samples T test in SPSS 20.0 (IBM Corp., 2011) because the quantity of sample from other districts were too small to compare.