Cytokeratin 5 (CK5) is related to cytokeratin 6. They have similar tissue distribution and present in different proportions in many non-keratinized stratified squamous epithelium, such as tongue mucosa, tracheal basal epithelium, epidermal basal cells, hair follicles, skin sebaceous glands and sweat glands, breast cavity cells, prostate basal cells, urethral epithelial cells, vaginal and cervical endometrial mucosa. Cytokeratin 5 and Cytokeratin 6 are also expressed in basal cell epithelioma, cutaneous squamous cell carcinoma, tongue, epiglottis and rectoanal region.