Icing is useful for acute musculoskeletal injuries and inflammatory conditions and is widely practiced by athletes. To achieve maximum benefit from icing, the injured or inflamed tissues must be sufficiently chilled without causing frostbite.

Frostbite occurs when tissue is cooled below its freezing point, and it is important to realize that tissue freezes in a temperature range in the upper 20's, Fahrenheit. Therefore, if tissue is chilled to 32° F, the freezing point of water, frostbite will not occur.

The safest and most reliable way of accomplishing this is with ice water. When ice and water are present together in the same container, the temperature of the water remains at 32° F until the ice melts. The same cannot be said of freezer packs or gel packs, which are unfortunately widely used for "icing." These come out of the freezer at freezer temperature, which is about 0 to 5° F, and their temperature gradually increases during use. Their temperature does not plateau at 32° F, like that of ice while it is melting. So with freezer packs, their initial temperature is cold enough to cause frostbite. Most people therefore end up placing an insulating layer between the pack and the skin, but then you still don’t know the temperature to which the skin is being exposed. It could be below the tissue freezing point, therefore causing damage, or it could be so warm that not too much tissue cooling is happening at all.

This latter phenomenon is especially common when icing children’s injuries. They find the cold uncomfortable and will ask for thicker insulation between their skin and the freezer pack. Naturally, not wanting to cause frostbite, we comply with their request, often to the point that very little beneficial cooling is occurring.

The use of ice water avoids these problems.  Avoid directly applying ice straight from the freezer, however, as it does come out of the freezer at freezer temperature (about 0 to 5° F). The ice massage technique calls for this and can cause frostbite. Instead, either place the ice in a plastic bag (watertight variety, like Ziploc) and add water, or pack it into a ball in a towel and run this under the tap water until thoroughly wet.

When using the Ziploc method, a Ziploc freezer bag, or equivalent, prevents most leakage episodes.  Fill the bag halfway with ice, then with cold tap water until about the 3/4 level is reached.  The bag will begin to bulge.  Place it on the countertop and simultaneously squeeze out the remaining air while zipping closed.  By not overfilling the bag, it is less likely to pop open, and it remains pliable, conforming to the injured area.  Apply directly to the skin.  Children may find the cold sensation to be too extreme, so they may require the use of a thin insulating layer, something like the thickness of a cloth napkin, although this is not medically necessary.

Ice for 20 to 30 minutes per session. Some athletes will ice 20 minutes, remove the ice for 20 minutes, and ice another 20. For greatest effectiveness, icing should be done at least twice a day. Many athletes are able to keep the swelling down in more severe injuries by icing several times a day or even continuously. Continuous icing carries the risk of prolonged tissue ischemia, or at least relative ischemia.  A recent report of acute compartment syndrome after continuous circumferential icing at 40° F (temperature-controlled icing apparatus) blamed the tissue damage which led to the compartment syndrome on frostbite, which is of course impossible.  However, it is possible that the tissue was perfused less than that which was necessary for its survival.  Pressure from the circumferential cuff may also have contributed.  For this reason, intermittent icing is probably preferred over continuous.