The article provides a comprehensive overview of human keratins, focusing on their biology and pathology. Keratins are intermediate filament proteins found in epithelial cells, with 54 functional genes in humans. These proteins form heteropolymeric filaments by pairing type I and type II molecules and play crucial roles in the mechanical stability and integrity of epithelial cells and tissues. They also have regulatory functions, such as protecting cells from stress, promoting wound healing, and regulating apoptosis. The article discusses the expression patterns of keratins in different cell types and tissues, their functional significance in transgenic mouse models and human hereditary keratin diseases, and their importance in tumor diagnosis and classification. Keratins are particularly useful in distinguishing between different types of carcinomas, especially in cases of unclear metastases. The article also highlights the clinical applications of keratins, including their use as tumor markers and in monitoring cancer progression and response to therapy.The article provides a comprehensive overview of human keratins, focusing on their biology and pathology. Keratins are intermediate filament proteins found in epithelial cells, with 54 functional genes in humans. These proteins form heteropolymeric filaments by pairing type I and type II molecules and play crucial roles in the mechanical stability and integrity of epithelial cells and tissues. They also have regulatory functions, such as protecting cells from stress, promoting wound healing, and regulating apoptosis. The article discusses the expression patterns of keratins in different cell types and tissues, their functional significance in transgenic mouse models and human hereditary keratin diseases, and their importance in tumor diagnosis and classification. Keratins are particularly useful in distinguishing between different types of carcinomas, especially in cases of unclear metastases. The article also highlights the clinical applications of keratins, including their use as tumor markers and in monitoring cancer progression and response to therapy.