A few months ago, I set out to test cold showers. Here's what I wrote for my experimental mission statement:

People are raving about what hormetic opponent process magic silver bullet it is to take cold showers. A little research gave supposed benefits of increasing circulation, mood, immunity, fertility, energy, exercise recovery, fat loss, mental alertness, pain and stress tolerance, cold tolerance, and skin and hair health. They're even supposed to stop depression and hair loss and tumors. I'm going to alternate two weeks of cold showers with two weeks of hot showers for the next two months and see what actually happens.

So excepting two days of each condition when traveling, every day for two months I woke up, did a 10-minute workout, immediately took a 7-minute shower, recorded my energy, mood, and shower discomfort, and took an 8-minute Quantified Mind battery. This wouldn't tell me anything about skin health and tumors, but it would get the main thing: does a cold shower begin one's day more vigorously than a hot shower?

Results

There were no observable differences on any Quantified Mind tests, suggesting that the brain does not care about the water temperature.

Nor was there any difference in self-reported energy levels when I pasted the data into Statwing:

But it did seem to make me happier immediately afterward:

That's something, I guess. I don't yet know if it makes up for the apprehension of getting into the shower in the first place. The difficulty and shiver latency of jumping into the cold shower went down as I got toward the end of each two-week period as I got used to it until it wasn't that big a deal.

What I realized from doing this is that seven-minutes is too short for an enjoyable hot shower and way too long for a cold shower. The advantage of the cold shower is that I can do it in under a minute (since I don't use any shower products). The experiment called for normalized shower times, but after it ended, I just started doing long hot showers sometimes and instantaneous cold showers other times. Since it takes three minutes for the water to heat up in this apartment, it's often more convenient to go cold and fast, now that I'm practiced.

Cold showers: slight evidence that they're good, but not magical.

Caveat: I don't think the water in my shower goes as cold as that of the most ravenous cold-shower bloggers.