Hot shower can help to kick colds, soothe pain, and moisturize skin.
Cold showers increase alertness, make hair appear shinier and stronger, improve immunity and circulation, relieve depression and ease stress.
As showering includes raising the arms above the head, this puts an extra workload on the heart known as the pressor response (increase in blood pressure) and may be exhausting for heart patients. Heart attack survivors are permitted to take unsupervised showers (with warm not hot water) in later stages of rehabilitation (level 7, when permitted to walk up one flight of stairs under supervision).
Taking a shower burns 3.5 METs/hr equivalent to moderate intensity activities like mopping floors or bowling.