Icing injuries prolongs pain and slows recovery, researchers find

An ice pack on a swollen ankle can feel like the most obvious cure in the world. It dulls pain, reduces swelling, and has been part of sports and first-aid advice for decades. But new research from McGill University suggests that quick relief may come with a tradeoff. In mice, icing eased pain early on, yet it also stretched recovery much longer than expected.

The work, published in Anesthesiology, points to a problem that is starting to surface across pain research. Treatments that tamp down inflammation can make people or animals feel better right away, but inflammation is also part of the body’s repair process. Shut too much of it down, and healing may not unfold the way it should.

“These results highlight a paradox: treatments that reduce inflammation and relieve pain in the short term may, in some cases, interfere with the biological processes required for full recovery,” said lead author Lucas Lima, a research associate at the Alan Edwards Centre for Research on Pain.

That tension sits at the center of the new findings.

Icing, or cryotherapy, remains a standard response to sprains, strains, and sore muscles. It is built into the familiar RICE protocol, short for rest, ice, compression, and elevation. Athletes use it. Clinicians recommend it. So do plenty of parents, coaches, and weekend runners. Yet the McGill team says the long-term evidence behind that practice is thinner than many people assume.

To test what icing does beyond the first wave of pain, the researchers used two mouse models of acute inflammatory pain. In one, they created local paw inflammation using complete Freund’s adjuvant. In the other, they used an exercise-enhanced pain model involving hypotonic saline injected into the gastrocnemius muscle before and after wheel running.

The animals then underwent water-based hind paw cooling for 30 to 60 minutes. The cooling was applied during the first three days after injury, using different timing schedules. After that, the team tracked nociceptive sensitivity, or pain-related responses, using three behavioral measures over more than 30 days.

The pattern was striking. Cryotherapy prolonged pain behavior by about two-fold. Instead of resolving in roughly 15 days, pain lasted more than 30 days.

That result matters because icing is usually sold as a way to speed recovery, or at least help support it. Here, it did the opposite.

The study also offered evidence for how that might happen. When the researchers injected exogenous neutrophils, a type of white blood cell involved in inflammation and tissue response, into the affected hind paw early on, the pain chronification caused by cryotherapy was reversed. That finding suggests the cold treatment may be interfering with immune activity that helps pain resolve.

Senior author Jeffrey Mogil, James McGill Distinguished Professor and E. P. Taylor Chair in Pain Studies, said the work points to a larger question about when anti-inflammatory strategies are actually useful.

“Our results suggest we need to better understand when anti-inflammatory strategies are helpful and when they are not,” Mogil said.

The McGill findings do not stand alone. Lima said they add to a growing body of research that questions whether familiar anti-inflammatory approaches always help in the long run. Previous studies have shown that acetylsalicylic acid, better known as Aspirin, can extend the duration of pain. Other animal work has also suggested that icing may delay tissue repair.

What makes the new study notable is its focus on pain duration itself. According to the researchers, this is the first direct evidence that icing can lengthen how long pain lasts, at least in experiments designed to mimic inflammatory and exercise-related injuries.

That is an uncomfortable idea, partly because icing feels so intuitive. Pain and swelling are usually taken as signs that something is wrong and needs to be suppressed. But the body’s inflammatory response is not just damage. It is also activity, signaling, and cleanup. In that view, reducing inflammation too aggressively may interrupt steps that are needed for real recovery.

The study’s other results sharpen that point. Heat did not affect pain resolution. Menthol did not either. Nor did contrast therapy, which alternates heat and cold. Those treatments did not appear to push recovery off course the way cryotherapy did in these experiments.

One sentence in the study’s conclusion cuts straight to the issue: cryotherapy, like steroid and nonsteroidal anti-inflammatory drugs, may need to be reconsidered in the management of acute inflammatory injury.

The researchers are careful not to overstate what the mouse data mean. Mogil emphasized that the results are not yet directly applicable to humans. That caution matters. A treatment can behave one way in animals and another way in clinical care, where injuries vary, dosing differs, and patients bring age, health history, and other factors into recovery.

Still, the work raises a clear challenge to a deeply rooted habit.

A clinical trial is already underway to see whether a similar effect appears in people recovering from procedures such as wisdom tooth removal. That next step is important because it moves the question from a controlled lab setting into a common real-world form of inflammatory pain.

For now, the study does not say that every ice pack is harmful, or that nobody should ever use one. It does not test every kind of injury, and it does not prove the same timeline would hold in people with sprains, pulled muscles, or post-exercise soreness. What it does say is narrower and more provocative: in mice, icing reduced pain in the short term but also delayed the process that brings pain to an end.

That may help explain why the debate over inflammation has changed in recent years. The older instinct was simple, calm the inflammation and recovery will improve. The newer view is messier. Some inflammation may be part of the cure.

If that turns out to be true in humans as well, then one of the most common pieces of injury advice in modern life may need a serious second look.

Research findings are available online in the journal Anesthesiology.

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