Gold nanoparticles have gained significant attention due to their ease of synthesis, chemical stability, and unique optical properties, making them promising for biomedical applications such as chemical sensing, biological imaging, drug delivery, and cancer treatment. However, understanding their potential toxicity and health impact is crucial before clinical use. This Perspective reviews recent findings on the toxicity of gold nanoparticles in vitro and in vivo, highlighting the importance of interactions with physiological fluids and the need for controlled experiments to understand their biological impact. The authors discuss methods for assessing cellular uptake and toxicity, emphasizing the variability in results due to factors like particle size, shape, surface chemistry, and cell type. They also explore strategies to mitigate toxicity, such as modifying surface chemistry and controlling nanoparticle aggregation. The review concludes with a call for more comprehensive studies to address the full range of nanoparticle properties and their effects on biological systems.Gold nanoparticles have gained significant attention due to their ease of synthesis, chemical stability, and unique optical properties, making them promising for biomedical applications such as chemical sensing, biological imaging, drug delivery, and cancer treatment. However, understanding their potential toxicity and health impact is crucial before clinical use. This Perspective reviews recent findings on the toxicity of gold nanoparticles in vitro and in vivo, highlighting the importance of interactions with physiological fluids and the need for controlled experiments to understand their biological impact. The authors discuss methods for assessing cellular uptake and toxicity, emphasizing the variability in results due to factors like particle size, shape, surface chemistry, and cell type. They also explore strategies to mitigate toxicity, such as modifying surface chemistry and controlling nanoparticle aggregation. The review concludes with a call for more comprehensive studies to address the full range of nanoparticle properties and their effects on biological systems.