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Icing an Injury Is Not an Old Rat's Tale

Most people know to put ice on an injury as soon as possible. This goes for sprains, strains, bruises, and dislocations. Not all of us understand why. Even researchers are still studying this question.

The obvious reason is that ice is thought to keep the swelling down. Of course, the freezing sensation takes our minds off the pain, too. But why does 20 minutes of ice applied in the first 30 minutes of an injury have a continued effect five hours later? What is happening in the blood vessels and in the cells?

Researchers at Wake Forest University School of Medicine (North Carolina) studied injuries in rats to answer this question. They started with the basic idea that cold causes the blood vessels to close down. This is called vasoconstriction. This prevents swelling and damage from bleeding in the injured tissue.

Using high-tech microscopes, the scientists were able to see what happens to an injury. They could watch the response right away and monitor it for minutes to hours. Using a special dye, they could see right down to the white blood cell level.

Normally, white blood cells (WBCs) move to an injured area to help repair the area. These cells move like an amoeba, rolling and sliding along the inner lining of the blood vessels. Swelling or edema occurs when WBCs stick to the wall of the blood vessel. Too many WBCs rolling along the blood vessel also cause damage and edema. Ice applied 15 minutes after the injury reduces this rolling and sticking of the WBCs. The effect is long lasting, sometimes up to several hours later.

References: D. Nicole Deal, MD, et al. Ice Reduces Edema: A Study of Microvascular Permeability in Rats. In The Journal of Bone and Joint Surgery. September 2002. Vol. 84-A. No. 9. Pp. 1573-1578.

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