I would say the majority of patients I see in practice are unsure as to whether they should use hot or cold in the management of their injury.
In the acute phase, the first seven days of injury, you are likely to be suffering pain, swelling, limited mobility, and maybe some bruising. You should be reaching for a COLD PACK, and applying for a good 20 minutes. Why? The cold will reduce pain, blood flow, swelling and tissue metabolism.
In the subacute and chronic phase, after seven to ten days post injury, you should be in less pain, have better function and reduced swelling. You should be reaching for a HEAT PACK, and applying for a good 20 minutes. Why? Blood flow is increased, as well promoting greater metabolic rate and tissue extensibility. Heat also increases oxygen uptake and accelerates tissue healing. Destructive enzyme activity is also increased to process damaged proteins.
If unsure, then always seek the advice from a qualified health professional, as applying the wrong modality can make your symptoms worse.