It is important to end a contrast bath with a soak in cold water to help reduce swelling.
These baths can be continued at least daily for up to 2 weeks. But if swelling and bruising last this long, a doctor should be consulted.
There is not much evidence that contrast baths work better than ice, but the theory is that changing the temperature back and forth between cold and warm creates a kind of pump. Heat causes blood vessels to get bigger and cold causes them to get smaller. Alternating between heat and cold means the blood vessels alternate between bigger and smaller. This change in blood movement could help reduce inflammation and swelling, and that could improve range of motion in the joint.
WebMD Medical Reference from Healthwise