The process is a reasonably straight-forward polymerization of unsaturated fatty acids. So yes, there will be some carcinogenic compounds created, you should no

The process is a reasonably straight-forward polymerization of unsaturated fatty acids. So yes, there will be some carcinogenic compounds created, you should not ingest too many of those. However you have to remember that correctly seasoning an iron pan does not create a coating or a layer as such, the polymerized oil fills in the microscopic gaps in the metal and creates a smoother surface, with fewer irregularities that proteins and carbs can cling onto. The actual amount of polymerized oil left on a correctly seasoned pan is absolutely minuscule, so if anyone complains that their seasoning is flaking off, they tried to slather on a way too thick layer, treating it more like a paint or lacquer than a surface treatment. Compare that to the teflon coating on a non-stick pan, which is an actual thickness of material bonded onto the metal surface of the pan, in fact sprayed on much like paint or powder coat, which is why it will eventually start flaking off. Seasoning is not the burnt bits in the pan after you fry something, it's a process that binds polymerized fat molecules into the surface of the iron itself, which is why you can't simply scrub it out with dish soap. If you somehow can, it's just burnt bits, not seasoning. I had to take sand paper and a not insignificant amount of elbow grease to a second-hand cast iron pan I was stripping down, in order to get down to bare metal, but the actual amount of material I sanded off was less than a quarter teaspoon of black dust. That tells you something about how little material actually goes into seasoning cast iron, and how hard it bonds to the iron. If you eat fried or grilled meat and enjoy that heavy maillard reaction on the surface, and especially if you like your BBQ sauce to get dark and sticky and aaaalmost burnt, you're already ingesting significantly more carcinogens than you would ever get from a cast iron pan.