This article, authored by a team of experts from various institutions, reviews the potential risks associated with engineered nanoparticles (NPs). The review highlights the increasing research on the toxicological properties of NPs and the ongoing international efforts to gather more technical and toxicological data. NPs can be deposited in the respiratory tract after inhalation, leading to oxidative stress and inflammatory reactions, and even tumor-related effects in rats. Some NPs can cross the blood-brain barrier and enter the systemic circulation, though the extent of translocation is still debated. Dermal exposure to metal oxide NPs used in sunscreens has shown limited evidence of systemic exposure, but the adequacy of current testing methods is questioned. Oral uptake of NPs in the gastrointestinal tract is well-established, particularly in food and pharmaceutical applications. However, the toxicity of new chemical and physical properties of engineered NPs is unknown, and limited ecotoxicological data precludes a systematic assessment of their impact on ecosystems. The article also discusses the production and application of NPs, emphasizing the need for standards and terminology to support risk assessment and regulation. It outlines the challenges in characterizing and assessing NP exposure, particularly in occupational settings, and recommends the development of systematic review methods and harmonized measurement strategies.This article, authored by a team of experts from various institutions, reviews the potential risks associated with engineered nanoparticles (NPs). The review highlights the increasing research on the toxicological properties of NPs and the ongoing international efforts to gather more technical and toxicological data. NPs can be deposited in the respiratory tract after inhalation, leading to oxidative stress and inflammatory reactions, and even tumor-related effects in rats. Some NPs can cross the blood-brain barrier and enter the systemic circulation, though the extent of translocation is still debated. Dermal exposure to metal oxide NPs used in sunscreens has shown limited evidence of systemic exposure, but the adequacy of current testing methods is questioned. Oral uptake of NPs in the gastrointestinal tract is well-established, particularly in food and pharmaceutical applications. However, the toxicity of new chemical and physical properties of engineered NPs is unknown, and limited ecotoxicological data precludes a systematic assessment of their impact on ecosystems. The article also discusses the production and application of NPs, emphasizing the need for standards and terminology to support risk assessment and regulation. It outlines the challenges in characterizing and assessing NP exposure, particularly in occupational settings, and recommends the development of systematic review methods and harmonized measurement strategies.