One of the most frequent questions I hear is “When do I use heat and when do I use ice?” for injuries. It’s a good question. And the tendency is to give a black and white answer, which I have found over the years is not always the correct answer. However, generally speaking you use ice for an acute (recent) injury and heat for a chronic injury or pain. Having said that, let’s look at the reasons so that you’ll never need to ask the question again, and you’ll always know what to do.
Use ice for acute injuries.
You always use ice for an acute injury. But what is acute? Acute means that there is a very active inflammatory process occurring in the area of the injury. Imagine having twisted your ankle. The ankle has started to swell up, get red and hot, and really hurt. Ice at this stage is an excellent way to control the inflammation and pain. Ice will reduce the amount of swelling and directly reduces the heat. Elevating your ankle (above your heart) will also help reduce the swelling by making it easier for lymph and blood to flow back to the heart.
Applying ice is best done with an ice pack that stays soft but cold. Don’t put ice directly on your skin. Don’t even put a pack of frozen corn directly on your skin. Use a towel or cloth to lessen the cold. Apply the ice pack for 30 minutes to a couple hours at a time, depending on the severity of the injury. But be sure not to give yourself frost bite. You shouldn’t start to feel numb because of the cold. If you do, you’re over using the cold pack.
How long do you use ice?
You use ice as long as there is active swelling, but not for more than one to three days. For instance, using the example of the ankle above, you’ll start to see the swelling go down-the size of the ankle lessens. You’ll feel less heat when you touch the skin over the injury. You’ll also feel the pain lessening. When you do feel it getting better in this way, it’s time to let on using the ice packs. The exception is when you keep re-injuring the same area. If you continue to walk around on the injured ankle, you’re going to continue injuring it and the swelling will not go down as fast. In this case you want to continue using the ice until the swelling is noticeably better, the ankle is less hot and not as painful.
How about using heat?
Heat is not used for recent or acute injuries. But many people suffer from chronic pain that is due to what can be thought of as an ongoing low grade injury. Take someone with chronic neck pain a couple of years after a car accident. In the accident their neck suffered a whiplash injury. This means that there was injury to the soft tissues of the neck-including the muscles, the tendons, ligaments, even the discs. These injuries can take a long time to heal. Researchers have found that the body continues to rebuild the injured tissue for two to five years after such an injury. The injury is no longer in an acute stage, but there may be low grade inflammation occurring never-the-less. The difference is that such inflammation is not going to be helped by ice applied to the skin. The structures that are inflamed are to deep to be affected by an ice pack applied to the skin surface.
Chronic pain usually also involves muscles. Muscles become stiff, tight and sore. This constant tightness of the muscles restricts blood flow in the muscles. As a result metabolic toxins build up in the muscles. You may have heard of lactic acid. Lactic acid builds up in muscles when there is insufficient blood supply and oxygen supply to the muscle. And lactic acid will also make muscles sore and painful. There are other chemicals which build up in muscles too, that produce soreness.
Using heat can promote blood flow and oxygen supply to the muscles.
Applying heat to sore and tight muscles increases blood flow to the area. With increased blood flow also comes more oxygen. The nutrients in the blood and the oxygen help the healing process of injured muscles. More blood flow in also means more blood flow out. And with the increased outflow of blood, toxins like lactic acid and other chemicals which cause chronic muscle soreness and stiffness are removed. This is why after applying heat to a sore neck it often feels better.
The other thing about heat and cold.
There’s another thing about applying heat and/or cold. When you have an injury and pain, you feel the pain only if it registers in your brain. If you had ankle pain right now and the pain nerve from the ankle was cut, the pain would disappear. To feel pain the pain nerve has to transmit its signal to the spinal cord where another group of nerves carries it to the brain.
The interesting thing is that there is competition for use of the circuits transmitting information up the spinal cord to the brain. After all, when you have pain you don’t stop feeling other sensations from the area of pain. You would still feel someone’s touch, or hot or cold, or even movement of the area. (The feeling of movement is also a “sense”. Imagine moving your injured ankle with your eyes closed. You would still be able to feel it, right? That’s because of sensory nerves that transmit the sense of movement and position to your brain.)
This reality of competition for transmission of sensory input to the brain at the spinal cord level can be used to our advantage. Let’s go back to the example of the injured painful ankle. Applying a cold pack reduces pain first by helping to control the inflammation. But second it does so by competing with the pain signal that are trying to reach the brain. Because of the high demand for the circuits to the brain (cold sensation competing with pain sensation) some of the pain signals don’t get transmitted. The result is less pain (in our experience). Nothing else has changed, just the fact that fewer pain signals are reaching the brain, so we feel less pain.
This principal is behind the use of TENS (trans-cutaneous electrical nerve stimulation) units. These devices stimulate nerves that compete with pain nerves. As a result fewer pain messages get through and we feel less pain. The bottom line is that you can use ice and/or heat to do the same thing. That is why I sometimes have a patient say to me that they prefer ice on chronic muscle stiffness-for them it blocks more of the pain signals than heat does, so they get better relief from it. So in the end you can use hot packs and/or cold packs for chronic aches and pains, depending on your preference. I prefer hot packs because it promotes blood flow as I discussed above.