Thats because of how the body reacts to heat or cold. The hor water never changes in temprature, but your body whem standimg under it has time to realise there is hot water and kick in cooling measures. Blood will be flushed close to the skin (you see redness) in order to dissapate heat to outside the body, and many other methods of dealing with heat. TLDR: heat doesnt change. Your nody just gets used to it as opposed to being shocked by sudden heat
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