I’ve heard something about this before and I think it is true but I am not sure why.
There is also evidence that people with red hair are less sensitive to pain than other people. I think this is because the genes of people with red hair mean that they respond differently to a set of pain relieving hormones called endorphins.
I am not sure if the two things are connected. However, if you do need an operation, they have very good ways to tell how much anesthetic you will need so I’m sure the doctors will know what to do!