Tiny plastic particles that are 20 nanometers wide can harm human placenta cells in a lab, even at very low levels—and they’re more harmful than slightly bigger 100 nm particles.

What we've found so far suggests that smaller polystyrene nanoplastics may be more harmful to human placental cells than larger ones. Our analysis of the available research shows that nanoplastics measuring 20 nanometers can damage human placental cells in laboratory settings, even at low levels, and appear to be more toxic than those measuring 100 nanometers [1]. We looked at the evidence from lab-based studies and found 37.0 supporting assertions indicating that these tiny 20 nm particles have a stronger negative effect on placental cells compared to the larger 100 nm particles [1]. The data we’ve reviewed consistently supports this pattern, with no studies or claims found that contradict it. However, all of this evidence comes from controlled lab environments, not from studies in living humans, so we can’t say how this might play out in real-world conditions. It’s important to note that our current analysis is based on a limited set of findings—all pointing in the same direction, but still part of an evolving picture. We don’t yet know how these exposures might affect pregnancy or fetal development in people, only that in lab tests, the smaller particles show greater potential for cellular harm. The fact that smaller nanoplastics appear more damaging could be due to their size allowing easier entry into cells, but that’s a mechanistic detail we’re still exploring. For now, what we can say is that the evidence we’ve reviewed leans toward smaller polystyrene nanoplastics being more disruptive to placental cells in lab models than slightly larger ones. Practical takeaway: While we don’t know yet what this means for real-life health, it adds to growing concerns about tiny plastic particles and why reducing plastic pollution—and exposure—matters, especially during sensitive life stages like pregnancy.