Cold plunges are all the rage. But what does the science say?

The cold plunge has entered the mainstream in recent years, along with lofty claims about supposed health benefits, from reducing inflammation and boosting immunity to alleviating depression and anxiety. But is there any science behind it? Or is this just a lot of hype? 

Cold plunges are all the rage. But what does the science say?
A large crowd of people, including one carrying a Canadian flag, run into icy water.

The cold plunge has entered the mainstream in recent years, along with lofty claims about supposed health benefits, from reducing inflammation and boosting immunity to alleviating depression and anxiety. But is there any science behind it? Or is this just a lot of hype?