When to Use Ice on an Injury, and When to Use Heat

This post is part of our Home Remedy Handbook, a tour of the landscape of home remedies from the iffy to the doctor-approved. Read more here.

Hot packs and cold packs are some of the most useful and convenient tools we have for dealing with pain in specific body parts. But when should you use each one?

Ice is commonly used for minor injuries, like ankle sprains and pulled muscles, but you may have heard that it’s no longer recommended as much as it used to be. Many of us learned that injuries should be addressed with the acronym RICE: Rest, Ice, Compression, and Elevation. But in recent years, you may have heard more about its opposite, METH: Movement, Elevation, Traction, Heat.

In truth, there are good times for ice and good times for heat. Let’s look at what each one does, and go over a few rules of thumb to help you decide which one to use.

Why you have swelling and inflammation after an injury

When you get a sudden injury, like an ankle sprain, your body turns on a process called inflammation. Inflammation causes the injured area to become red, swollen, hot, and extra painful. This isn’t fun to experience, but it’s how the healing process begins.

The swelling brings extra immune cells to the area to get the repair work started. Swelling can also make the body part stiff, which may be somewhat beneficial for protecting the area. And the pain can result in you naturally giving the injured area some rest.

But that doesn’t mean that inflammation is always good. If the swelling is extreme, it can cause more damage. And while pain can stop us from using the injured body part, we’re usually happier if we can take the edge off the pain and simply not use the body part anyway.

What happens in your body when you apply ice

Ice reduces a lot of these aspects of inflammation. It numbs pain, and honestly—the main reason we use ice for injuries is as a cheap, quick, easy form of pain management. It keeps your body from being able to swell the tissues as much as it otherwise would, and it can reduce the formation of bruises and hematomas (blood clots in the tissue).

In those first few hours to days after an injury, ice can be helpful to control that potential overreaction. Your ankle can heal just fine with a little bit of swelling; it doesn’t necessarily need as much swelling as your overzealous immune system might want to give you.

There are downsides to ice, of course. Once the injury is in the past and swelling has gone down, you don’t want to get in the way of your body’s healing processes. Ice can also increase pain for some injuries, especially muscle soreness, cramps, or knots. It tends to make stiffness and muscle cramps worse.

You also need to be careful with the ice. Cooling the area is good; giving yourself frostbite is not. A good rule of thumb on when to take a break from the ice pack is, “when you’re numb, you’re done.” If the skin is numb, take the ice pack off for 20 minutes or so. Never let yourself fall asleep with an ice pack on.

What happens in your body when you apply heat

Heat’s effects are, unsurprisingly, the opposite of ice. Heat dilates blood vessels and increases blood flow, so if you were to apply heat to that ankle sprain, you could increase swelling and possibly make the injury feel more painful.

But after that initial inflammation (or for an injury that came on gradually and didn’t pass through that stage), heat can be a good thing. The increased blood flow can promote healing. This is where the METH acronym comes in: movement and heat are especially helpful for moving blood and nutrients to where they need to go, and for keeping the injured body part from getting too stiff or painful as it heals.

Heat can also reduce soreness and stiffness in muscle injuries. If your back muscles are sore after a heavy deadlift workout, heat will feel great on your back. If you woke up with a crick in your neck and now your neck muscles feel stiff, heat will likely provide some relief.

How to know which to use

One rule of thumb is that ice is for the first 24 (or 48, or 72) hours after an injury, and heat is your better bet afterward. This isn’t a bad rule, but there’s nuance to it.

First of all, how long is that initial period where you should ice it? That will depend on the injury. For some, it’s just a few hours long. For others, especially more serious injuries, it may indeed last several days. A good way to tell is to ask yourself if the injured area is red, hot, and unusually swollen and painful. If so, it’s ice time. If not, you can probably move on to heat.

Another important consideration is what type of pain or injury you’re dealing with. The injuries that respond well to ice are usually acute tissue damage: something got torn, broken, or pulled. The ones that respond to heat are more likely to be chronic or nagging pains, or ones that involve spasms or cramps. A few examples:

As a very general rule, you can go with your gut. When my back muscles are sore after a workout, I want nothing more than to sink into a hot bath. You couldn’t pay me to ice them.

All of this advice is for minor aches and pains, by the way. Sometimes, injuries can be more complicated than what these simple rules account for. And if something is seriously wrong, or if you suspect it is, make sure to see a professional and follow their instructions. You don’t want to sit around icing that sprained ankle if it might actually be broken.