Pain management is handling of pain in soft and hard tissues of a body which is the result of either traumatic injury or overwork. It divides into acute and chronic pain. The pain here we are talking about does not include the pain from internal organs or malfunction of visera.

Acute pain is referred to when the injury happens within 24 hours. It accompanies with the 4 big signs --local heat, local redness, local edema/swelling, limited movement.

Chronic pain is called when the injury occurs more than 3 days ago or the pain lingers for years from overwork/overuse.

Cold compression is used for acute pain. It helps freeze the local blood circulation to ease up severe pain and swelling. 

Heat application is commonly used for chronic pain and tenderness. Coldness can kill pain, but it at the same time slows down the blood circulation which is not helpful for recovery. As the injury steps into chronic, there will be no local redness or bleeding. Therefore, The injured tissues are ready for recovery process. Oxygen and healthy blood flow is really important to get the problematic tissues healed. Therefore, we need heat to get the circulation going and oxygen delivered to feed the local tissues.