I noticed recently that UA has new headphones in F even on domestic routes that are nicer than the older ones for sure. I was dismayed when the FA announced that upon landing to put the headphones in the seat pocket so it is readily available for the next passenger. I would have assumed they at least go through some kind of sanitizing before the next use. I realized they are not not in plastic bags so for sure they are not cleaned. I know when I fly CX at least the headphones have a "sanitized" label, so even if they really did not do it I feel better about it.