You'll have to go to a medical library if you want actual medical journals. Many (most?) of those are not free online as they are in the business of making money.

But if you Google around you can find plenty of scholarly studies. Yes mixed in with the search results you'll find articles from people in the sauna business, but it's not all that.

There's also infra-red saunas that are supposed to be good. You can read this study if you like. http://link.springer.com/article/10....067-008-0977-y