DOS (dreaded orange spots) is the visible evidence of a fat or fatty acid turning rancid. Rancidity is a normal process that happens to any and all fats as they break down. It's a normal part of nature's recycling process.
Some fats go rancid much faster than others and there are some conditions and contaminants that cause rancidity to happen faster, but all natural fats will eventually break down and return to nature.
Fats that are mostly polyunsaturated are less stable than monounsaturated. Mostly monounsaturated fats are less stable than saturated.
