This review discusses the role of sialic acids in human health and disease. Sialic acids, a diverse family of sugar units, are typically found attached to the outermost ends of glycan chains on vertebrate cells and secreted proteins. Their negative charge and hydrophilicity contribute to various physiological and pathological processes. Sialic acids serve as binding sites for pathogens and toxins, and their presence is crucial for normal physiological functions such as charge repulsion in blood circulation and filtration in the glomerular basement membrane. They also play a role in pharmacology, where their presence can affect the half-life of glycoproteins in circulation. In fertilization and development, sialic acids influence interactions between sperm and the female reproductive tract. Genetic disorders related to sialic acid metabolism, such as hereditary inclusion body myopathy and sialuria, have been identified. Sialic acids are involved in immune responses, cardiovascular physiology, hematology, oncology, neuroscience, pulmonary medicine, endocrinology, nephrology, gastroenterology, hepatology, and dermatology. Recent advances include the discovery of sialic acid loss in hematopoietic stem cells and the role of sialic acids in the development of neurological disorders. The review highlights the importance of sialic acids in various biological systems and the need for further research to uncover their full range of functions.This review discusses the role of sialic acids in human health and disease. Sialic acids, a diverse family of sugar units, are typically found attached to the outermost ends of glycan chains on vertebrate cells and secreted proteins. Their negative charge and hydrophilicity contribute to various physiological and pathological processes. Sialic acids serve as binding sites for pathogens and toxins, and their presence is crucial for normal physiological functions such as charge repulsion in blood circulation and filtration in the glomerular basement membrane. They also play a role in pharmacology, where their presence can affect the half-life of glycoproteins in circulation. In fertilization and development, sialic acids influence interactions between sperm and the female reproductive tract. Genetic disorders related to sialic acid metabolism, such as hereditary inclusion body myopathy and sialuria, have been identified. Sialic acids are involved in immune responses, cardiovascular physiology, hematology, oncology, neuroscience, pulmonary medicine, endocrinology, nephrology, gastroenterology, hepatology, and dermatology. Recent advances include the discovery of sialic acid loss in hematopoietic stem cells and the role of sialic acids in the development of neurological disorders. The review highlights the importance of sialic acids in various biological systems and the need for further research to uncover their full range of functions.