There's a bit of a fad of taking cold showers for supposed health benefits (typically something about inflammation or circulation).

By 2040, will it generally be accepted that cold showers offer nonnegligible net health benefits to most people (i.e., not just helpful for some rare conditions)? This market will resolve "no" if there is some speculative evidece but it's not generally accepted. This market will resolve "yes" if the consensus in 2040 is that it was beneficial in 2023 (time of market creation) but these benefits no longer apply (due to, for instance, future medical advances make the point moot).

Obviously I mean "compared to normal, warm showers" – the point isn't to determine if there are health benefits associated with showering at all.