Without a doubt, this is one of the most frequently asked questions of physical therapists. They are also commonly misapplied. So in order to help explain what to use when, it is beneficial to first understand what exactly happens physiologically when you apply a hot pack or a cold pack.
Heat — A moist heating pad placed on the skin results in raising surface tissue temperature to between 104 and 113 degrees F. Once soft tissue reaches this temperature, the blood flow will increase to the heated area causing many therapeutic advantages including decreased pain and spasm.
Ice — Conversely, when a cold agent such as a cold pack is applied to an injured area, the underlying tissue temperatures are lowered and heat is removed from the body. Medically speaking, the immediate response is constriction (narrowing) of the blood vessels in the skin and reduction of blood flow thus decreasing acute inflammation and bleeding.
It is acceptable to use heat 24-48 hours after the injury. There are two kinds of superficial heat: moist and dry. Moist heat penetrates the skin and reaches the muscles, ligaments and joints. It is the moisture that penetrates and raises deeper tissue temperature. Examples include commercially manufactured electric heating pads that require you to dampen a sponge, microwavable wraps that can be moistened, or a heated wet towel. Dry heat typically elevates only superficial skin temperature. These might include non-moist electric pads or wraps and chemical thermal agents. Studies have shown that not only is moist heat more effective at reaching therapeutic levels but also is more comfortable.
Heat should be applied for 15-20 minutes maximum, checking the skin for redness or burning after the initial 5 minutes.
Ice is the preferred agent during the acute stage of inflammation (24-48 hours). There are a variety of sources that can be utilized as cold agents such as store-bought cold packs or a frozen bag of vegetables (i.e. peas conform nicely to joints). Conversely, homemade remedies like ice cubes in a plastic bag, ice soaked towels or a self-made gel-pack (freeze a self-sealing plastic bag with crushed ice and isopropyl alcohol at a 2:1 ratio) will also suffice.
Wrap any of these cold agents in a damp towel before applying on the affected area to protect the skin. Cold packs will remain at a sufficiently low temperature for 15-20 minutes. If longer treatment time is desired, then the pack should be replaced.
Heat or Ice?
Simple Questions to Ask Yourself:
• Is there swelling and pain? ICE
• Is there stiffness but no obvious swelling? HEAT
• Is this an acute injury (within first 48 hours)? ICE
• Are pain and swelling persisting (beyond the initial 48 hours period)? ICE
• Are you about to exercise? HEAT
• Are you sore from just finishing exercising? ICE
• Confused? ICE