Why can bleaching make oils more likely to become rancid?

Bleaching is a process used to remove pigments like chlorophyll and carotenoids from oils using agents such as fuller’s earth, activated carbon, or activated clays.1

While effective at decolorizing, bleaching can reduce an oil's resistance to rancidity. This occurs because the process inadvertently removes natural antioxidants along with the unwanted impurities. These antioxidants play a vital role in protecting the oil from oxidative degradation; without them, the oil becomes more susceptible to the chemical reactions that lead to rancidity.1