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 the freezing point of tissue is around 28° 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 pitfalls. Avoid directly applying ice straight from the freezer, however, as it does come out of the freezer at freezer temperature. 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 decreases the chance of leakage, although they still leak sometimes.  Fill to the halfway point with ice, then to the 3/4 level with cold tap water.  The bag will begin to bulge.  Place on the countertop and simultaneously zip closed while squeezing out the remaining air.  Apply directly to the skin.  Children may find the cold sensation to be too extreme, so they may benefit from having a thin insulating layer, about 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. However, continuous icing may compromise blood flow to tissues and result in damage.  There was a report in the medical literature in 2005, in which an athlete iced continuously with a temperature-controlled cuff apparatus, resulting in severe damage to muscle tissue.  It is possible that the pressure from the cuff contributed to this damage, but to be safe, it is recommended that intermitted icing be used rather than continuous.