Safety of brain heat exposure in sauna

I have been researching the brains response to heat and basically everything seems to indicate that excessive heat is bad for the brain. For instance Cell Phone related brain damage is attributed to microwaves heating the brain and creating FOS heat shock proteins. Also brain damage is believed to occur from overheating cause by other situations (heat stroke, MDMA users dancing until dehydrated the brain overheats).

I wonder what the verdict is for FIR (Far-Infrared-Sauna) head exposure? Some saunas have the head stick out but obviously the full chamber type heat your head and brain also. I have been using my dome type sauna on my face to treat a skin condition with great success but now I am concerned about overheating my brain.

I suppose this is also relevant to traditonal finnish saunas which can get up to 200f.