Heat and ice are effective modalities following an injury, but many people are unsure how to decide which to use.

Heating pads and other heat sources cause vasodilation of the blood vessels resulting in increased blood flow to the area. This can be helpful to relax sore or spasming muscles and is typically recommended prior to performing exercises to warm up the muscles. Your physical therapist may use heat at the beginning of the session prior to stretching or manual therapy. As a general rule, it is not a good idea to use heat over an area that is red, inflamed, or newly injured as this may cause increased swelling, pain and discomfort.

Conversely, ice causes vasoconstriction which results in decreased blood flow to the area. This is especially useful with an acute injury or over an area that is red, warm and inflamed such as a newly sprained ankle. It can also be helpful after exercise to prevent any pain and inflammation caused by increased activity.

To summarize, if the injured area is a muscle, if stiffness is a big complaint, or if the injury is more chronic in nature heat is probably the better choice. If the injury is acute (less than 7 days old), red, inflamed, or warm to touch, ice is a better choice. If you’re still unsure and the area is not warm to the touch, try both and use whichever feels best. It is important when using heat and ice to use them for no longer than 15-20 minutes at a time and continually check the skin underneath to ensure that it is not becoming irritated. Use extra caution when placing heat and ice over an area that has decreased sensation; these areas should be checked more frequently for skin irritation.