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It is common practice to use ice packs on injuries that cause bruising and swelling. It seems to be an effective method to assist in reducing swelling.

Why does ice reduce welling?

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related… – user4693 Nov 5 '13 at 6:59
It may be due to vasocostrictory effect of cooling. As vessels would constrict less fluid would be lost from the blood. – biogirl Nov 5 '13 at 15:31
@biogirl are you referring to the cells that enter the tissue during inflammation? – user4693 Nov 5 '13 at 15:32
I am referring to narrowing of blood vessels which would reduce both loss of fluid from the blood and the entry of WBCs in the area. – biogirl Nov 5 '13 at 15:35
there are also associated cells that bring fluid to the tissue when damaged – user4693 Nov 5 '13 at 15:38

Swelling is one of the signs of inflammation. Inflammation involves release of histamine by mast cells present in the tissues. Histamine causes vasodilation and leads to leakage of fluid from the blood, along with which neutrophils and other WBCs also enter the area. They phagocytose microbes that might have entered with the injury.

Applying ice would cause vasoconstriction* (i.e. narrowing of blood vessels.) which would reduce the leakage of tissue fluid and hence swelling.

*If you wonder why ice(or any cool thing) causes vasoconstriction think why you turn pale in winter ? Vasoconstriction reduces blood flow to the particular area and hence the exchange of heat is reduced which conserves body heat in cold environments.

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1+ I am going to ask another Q. I reckon you'll love it.! hang on, I'll write and post you a link – user4693 Nov 5 '13 at 15:58… – user4693 Nov 5 '13 at 16:07
Just to add to this- the recommendation for healing using ice is to alternate ice and warm packs so that the fluid exchanges, swelling and then constricting to aid healing - that's where a lot of the relief comes from. – shigeta Nov 5 '13 at 18:30

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