 The adult brain is protected by a tightly regulated environment, with cellular exchanges and diffusion restricted by tight junctions at interfaces between blood, brain, and cerebrospinal fluid, CSF. This environment is thought to be immature or leaky in infants and newborns, making them more susceptible to drugs or toxins entering their circulatory system from the mother. Some adult mechanisms, such as functional tight junctions and effective transporters, are present in both embryos and adults, while others are only present in embryos. Additionally, certain mechanisms unique to embryos, such as the transport of plasma proteins across the CSF blood barrier and intercellular junctions between neuro-apendymal cells lining the ventricles, are not present in adults. Furthermore, the developing brain's vessels are more fragile than those in adults, making it more susceptible to damage from drugs, toxins, and other pathologies. Finally, the placenta may also contribute to the neonates increased vulnerability by reducing its ability to remove toxic substances from the bloodstream. This article was authored by Norman Arsonders, Shane Alitalo, and Katarzyna Mzygieluska. We are article.tv, links in the description below.