Should you use ice or heat if you've pulled a back muscle or sprained an ankle, or have a chronic musculoskeletal condition? What you do can make a difference in your recovery.
When ice is nice
Ice an acute injury, such as a sprained ankle, until the swelling and pain subside, which usually takes two to three days. Icing constricts blood vessels so there's less internal bleeding and less leakage of fluids into tissues, thus lessening swelling and pain. It also acts as a local anesthetic and reduces muscle spasms.
Icing can help some chronic overuse injuries as well, including tennis elbow (and other types of tendinitis), certain types of knee pain, and bursitis, as well as persistent trigger point muscle pain. If you are an athlete or otherwise engage in regular vigorous exercise, icing the affected areas after workouts (your elbow after tennis, for example, or your shoulder after golf) may help reduce inflammation.
How to do it: A standard regimen is icing for 10 to 20 minutes every two to three waking hours. You can use ice cubes or crushed ice in a heavy plastic bag or wrapped in a towel, or use a commercial ice pack. Refreezable gel packs that remain flexible are good for wrapping around an injury (you can make your own by freezing a heavy-duty plastic bag partially filled with a mixture of one-quarter rubbing alcohol and three-quarters water). Instant cold packs, activated by twisting or squeezing, require no chilling.
To avoid skin damage, stop icing once skin is numb, and don't ice longer than 20 minutes at a time. Don't put an ice pack directly on the skin, especially on the elbow or outside knee, where the nerves are near the surface and can be damaged by prolonged exposure to cold; wrap the ice pack in a thin towel, or at least keep moving it. Don't use ice on blisters or open wounds. And don't use it if you are hypersensitive to cold or if you have an impairment of sensation or other circulatory problems, as in Raynaud's disease and often diabetes.
To minimize swelling, especially in severe injuries, use ice along with three other measures, often referred to as RICE: Rest (which reduces pain and helps prevent aggravating the injury), Ice, Compress (using a towel or elastic bandage wrapped snugly, but not too tightly, around the injury), and Elevate (hold the injured extremity above heart level to drain excess fluid). You can often combine ice and compression by holding the ice pack in place with an elastic bandage.
When to put on the heat
You can begin using heat after any swelling has subsided. Applying heat too soon may worsen initial inflammation. Heat dilates blood vessels and increases blood flow, which helps promote healing by removing waste products from the injured area. Heat also relaxes tight muscles, relieves spasms, reduces joint stiffness, lessens chronic inflammation, and has a general pain-relieving effect—and thus may be helpful for osteoarthritis and other recurring or chronic pain. There is some evidence that continuous low-level heat helps low-back, neck, and wrist pain.
How to do it: Use either dry heat (a heating pad or heat lamp, for example) or moist heat (a warm bath, whirlpool, or damp towel wrapped around a waterproof heating pad). Apply heat for 20 to 30 minutes, two or three times a day. Drugstores sell single-use or reusable thermal wraps that provide low-level heat for up to eight hours. There's no good evidence that moist heat is better than dry; use whichever you prefer.
The key word is "warm," not "hot." Don't use heat if there's an infection or loss of sensation. If pain or inflammation worsens, stop. If swelling develops, use cold instead.
When either or both may work
In general, ice what's swollen, and apply heat to what feels sore and achy. For low-back pain, there's no good evidence to favor either ice or heat—use whichever works best for you. Physical therapists sometimes alternate ice and heat ("contrast therapy") in treating low-back pain and other chronic injuries.
Note: Neither ice nor heat is a substitute for seeing your doctor for a serious injury or one that doesn’t respond to self-treatment.