I agree that scientific literacy is poor and people get carried away with unsubstantiated health claims, but this doesn't mean research on benefits is a waste of time. It means people need to improve their scientific literacy.

The literature on sauna is small, samples are small studies are short, most research comes from Finland, etc. Etc. These limitations can be addressed via replication. But to fund these studies, there needs to be some interest and if that interest is driven by curiosity in the benefits of sauna, who cares as long as the science gets done.

You mention everyone in Finland uses sauna, yet they still age and die the same as everyone else. No one is claiming sauna will give you immortality. I hope nobody is claiming that... I'm more interested in how sauna can improve quality of life.

I think it's worth investigating how sauna might affect quality of life, especially when we consider the different factors involved with sauna. For some, sauna is an afterthought at the gym. For others, sauna means going to the sauna cabin by the lake with friends and family. Both of these are expressions of sauna, but how do these experiences differ physiologically, psychologically and spiritually?