When you injure yourself, you may reach for a hot or a cold pack. Which option is better depends on the nature of your pain, what caused it and how long you've had it.
[...] Cold therapy should be used for injuries that result in swelling and inflammation such as joint sprains, muscle strains or bruises. The objective is to slow blood flow to the area and prevent the effects of the injury. Gel packs that can be kept in the freezer, coolant sprays or even a bag of frozen veggies will do the job.
It is important to avoid holding ice in direct contact with the skin for long periods as this can cause skin damage. It is best to wrap ice in a cloth and then apply it.
Cold therapy is most effective in the immediate or acute phase of pain when swelling and inflammation first kicks off. Typically, the treatment should be applied for about 20 minutes and can be reapplied every two hours for a few days. After that, the injury should be well into the healing phase and the swelling and inflammation will subside.
[...] Heat therapy is not recommended for acute management of sprains, strains or contusions as this promotes blood flow and can increase swelling and pain.
Heat therapy can help chronic conditions such as recurring joint pain, neck or back pain.
If pain is due to a strain or sprain, cold therapy should be applied immediately, but heat therapy can help relieve pain from 72 hours post-injury.
Heat therapy does not mean applying something very hot, rather it should be warm, pleasant and easily tolerated for long periods.
[...] The take-home message is that cold packs work well for reducing pain and inflammation in the acute phase of a strain, sprain or bruise—especially when used in as part of the RICE method.
Heat packs are useful for reducing muscle tension and stiffness and pain in the joints, but never in the initial phase of an injury. There is not enough evidence to show alternating the two is particularly useful, while cold water immersion therapy may help recovery after sport or sustained physical exertion.