Ice (cold therapy) is generally best in the first day or two after a fresh injury such as a sprain or strain, because it helps reduce swelling and numbs sharp pain. Wrap the ice or cold pack in a cloth and apply for around 15 to 20 minutes at a time, with breaks in between, never directly on bare skin.
Heat is usually more helpful for muscle tension, stiffness, and longer-standing aches such as chronic back pain or arthritis stiffness, because it relaxes muscles and improves blood flow. A warm bath, heat pad, or wrapped hot water bottle can ease these symptoms. Some people find alternating heat and cold helpful for ongoing pain.
Avoid heat on a fresh, swollen, or bruised injury, and avoid either treatment on broken skin or areas with reduced sensation, as burns or frostbite can occur without you noticing. If pain is severe, persistent, or accompanied by significant swelling, redness, or warmth, see a doctor, and a pharmacist can advise on pain relief.