Microplastics can carry endocrine-disrupting chemical additives and animal studies link them to inflammation. Definitive cause-and-effect in humans is still being established, so most environmental-health researchers recommend reducing exposure where it is practical rather than waiting for certainty.

The strongest human-health signal found so far was in a 2024 study of 304 patients found that those with microplastics in their carotid artery plaque were about 4.5× more likely to have a heart attack or stroke, or to die, over the next ~34 months than those without.

Microplastics have been found all over the human body including the heart, brain tissue, blood, lungs, breast milk, and placenta.