This review provides a comprehensive foundation for understanding nanoparticles, their sources, and their biological toxicity. It aims to inform public health concerns and raise awareness among scientists and manufacturers handling nanomaterials. The article highlights that humans have always been exposed to tiny particles through natural processes, and our bodies have evolved mechanisms to protect us from these intruders. However, the recent industrial and combustion-based advancements have increased anthropogenic particulate pollution, particularly nanoparticles, which have unique characteristics and can cause adverse health effects. The review discusses the classification of nanoparticles based on their dimensionality, morphology, composition, uniformity, and agglomeration. It emphasizes the distinction between nanostructured thin films and free nanoparticles, noting that the latter pose greater health risks due to their mobility. The toxicity of nanoparticles depends on various factors, including size, shape, composition, and surface properties. The article also explores the mechanisms by which nanoparticles can enter and damage the body, translocate within biological systems, and cause diseases such as asthma, bronchitis, emphysema, lung cancer, neurodegenerative diseases, and gastrointestinal disorders. The review concludes by highlighting the need for a rational, science-based approach to minimize the harm caused by nanoparticles while supporting continued research and industrial development. It emphasizes the importance of understanding the toxicology of each material and morphology to inform policy and regulatory processes.This review provides a comprehensive foundation for understanding nanoparticles, their sources, and their biological toxicity. It aims to inform public health concerns and raise awareness among scientists and manufacturers handling nanomaterials. The article highlights that humans have always been exposed to tiny particles through natural processes, and our bodies have evolved mechanisms to protect us from these intruders. However, the recent industrial and combustion-based advancements have increased anthropogenic particulate pollution, particularly nanoparticles, which have unique characteristics and can cause adverse health effects. The review discusses the classification of nanoparticles based on their dimensionality, morphology, composition, uniformity, and agglomeration. It emphasizes the distinction between nanostructured thin films and free nanoparticles, noting that the latter pose greater health risks due to their mobility. The toxicity of nanoparticles depends on various factors, including size, shape, composition, and surface properties. The article also explores the mechanisms by which nanoparticles can enter and damage the body, translocate within biological systems, and cause diseases such as asthma, bronchitis, emphysema, lung cancer, neurodegenerative diseases, and gastrointestinal disorders. The review concludes by highlighting the need for a rational, science-based approach to minimize the harm caused by nanoparticles while supporting continued research and industrial development. It emphasizes the importance of understanding the toxicology of each material and morphology to inform policy and regulatory processes.