The surface is lined by cuboidal and columnar cells with basophilic, clear, or lightly eosinophilic cytoplasm. Intraepithelial and subepithelial inflammatory cells, consisting predominantly of neutrophils, are nearly always a feature.

The nuclei are vesicular and there is a low N:C ratio. Importantly, there is a fair amount of nuclear variability. While not obvious in this image, nucleoli are also frequently seen.

Reactive atypia in the ductal epithelium is important to recognize in order to avoid misdiagnosis of dysplasia or carcinoma.