I started taking cold showers outside after my morning run when the heating element in the electric shower failed for the second time.

I just use a house and spray nozzle off the back-yard tap ( winter in Ireland is quite mild! ) and the main benefit I feel is the warmth when entering the house afterwards, rather than the typical step-out-of-shower chill.

After a couple of weeks it becomes a routine and normal showers now feel weak and insufficiently cleansing.

I haven't noticed any particular health benefits, still susceptible to colds and flu.