“Cold showers can have a mild anesthetic component, so when you flip the switch and turn to hot water, you could potentially expose yourself to water that is hotter than you realise.”

Source: https://www.huffingtonpost.co.uk/entry/shower-with-hot-and-cold-water_uk_63ca74f4e4b01e92886300f6

Cold showers only help for an instant effect, but a mild warm one can help gradually warm your body temperature so you’re not feeling overheated all day.

Source: https://www.nottinghampost.com/news/uk-world-news/eight-ways-keep-cool-wont-8511776