In all honesty, when I was young I thought that hot water is from Devils. It's water. But it's hot. Anyway looking back on history, for example, Mayans never went bald. Some people can think that besides what's recorded in history just by the way the word sounds when you hear it. Mayan. The men and women took baths, not showers, and they did that in lakes. The water people used to clean ourselves was always near the same temperature in the environment. If you shower with hot water on your hair, and then leave the shower... it's dry while you're in the shower but gets oily after. As for shampoos that are sold... they just delay the effect of hair becoming oily. Then it gets oily. Eventually it starts to fall. Of course people who aren't attacked with lethal fumes notice this much later, so it's a clever way of Devils causing hair loss. Now. As for cold water without shampoo. Your hair gets oily, or I guess oily-er when you exit the shower... but after a little bit of time... it actually gets really, really dry. As for room temp water, in reality I don't think when the earlier civilizations took baths they washed their hair that often... we had thicker hair. Sometimes experimentation can be the strongest form of proof. One month of frequent showers where you wash your hair, maybe during summer so you don't get a fever. Half the people picked hot water and shampoo, the other half picked cold water and no shampoo. A few chose room temp water. If you have not been attacked with these fumes it feels best, like a lake. It should be easy to adjust if you evenly turn the valves from cold and hot halfway, but for some reason someone has made machinery in a way a while ago that makes it difficult.