Why does ice reduce swelling?

To an average adult, you can say injury triggers inflammatory response where fluids migrate to the affected area. so if you put ice, you constrict their pathway, therefore preventing further fluid migration, and facilitating drainage of the fluid in due time. Ice has numbing effect too so there's pain reduction. But to a kid, just say that it's because of the ice princess. End of story. :-D just kidding!

When you sprain, strain, hyperextend, break, fracture ect... You have done trauma to some part of your body. Trauma causes the tissue around the part of your body to become inflamed which in other words means to swell and bruse. If you ice whatever part that you injured it calms the inflamed tissue and reduces the swelling. Hope this helped

How does ice work? Ice is a vasoconstrictor (causes a narrowing of the blood vessels) which can limit bleeding at the injured area. Ice also causes a pain relief effect by numbing the area that is applied too. Check this out: http://www.hacksports.com/v2/articles/wellington/ice.v.heat.htm