Normal metabolic processes produce reactive byproducts that damage proteins, leading to misfolding and aggregation.

“every time we breathe in oxygen and we're eating food and our mitochondria are trying to couple those together to generate energy well that generation of energy is really damaging because it also makes reactive byproducts that damage the proteins inside of our cell and when they damage the proteins the proteins become misfolded they're not their threedimensional structure is screwed up”