Nanotechnology has recently made significant inroads into diverse areas such as consumer products, healthcare, and environmental management. Nanochemicals exhibit distinctive properties that depend on their size, shape, composition, and degree of aggregation. These materials can be classified into organic-based, metal-based, and composite nanoparticles. As nanochemical production and usage increase, so does the potential for human and environmental exposure, raising concerns about their toxicity. This chapter explores the characteristics, uses, and toxicity of both metal- and non-metal-based nanochemicals. Such systems can accumulate in vital organs such as the heart, brain, kidneys, spleen, and liver following skin exposure, inhalation, and ingestion. Research, both in vitro and in vivo, indicates that nanochemicals can produce reactive oxygen species (ROS), which play a significant role in their toxic effects. Elevated ROS levels can cause inflammation, oxidative stress, and damage to membranes, cellular proteins, and DNA. Factors influencing ROS production include the surface properties, size, aggregation, shape, composition, solubility, and cellular uptake. Additionally, the toxicity of nanochemicals can vary based on their oxidation state, surface coatings, solubility, and physical form, and various environmental and health conditions.