Why does ice reduce swelling?
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Your body restricts blood flow to cold parts of your skin to conserve heat. When you dramatically cool down your skin with ice, your body reacts as if it’s in a cold environment and constricts blood vessels flowing into that area as if to conserve heat.
Swelling is the result of blood vessels dilating to bring additional blood and resources to a part of you that has been damaged. The constriction to “conserve heat” counteracts the dilation in response to damage so overall less blood flows into the area and swelling is reduced.
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Just to add to this very slightly
During the process of healing, your body will also produce heat due to increased cell metabolism in the injured area – that’s why, for example, a sprained ankle may feel slightly warm to the touch.
This heat can then have a knock on effect on said cell metabolism and make it slightly disordered and less effective. This can then increase scarring, and lengthen recovery times
By icing an injured area, especially in the early stages, you can displace a lot of the heat away from an injury. This has the effect of slowing cell metabolism and allowing it to be much more ordered, and therefore more effective at healing in an effective manner. This can reduce scarring and reduce recovery times.
This is also why we would place head injury / major trauma patients into a hypothermic state in many instances. Cool the brain down, slow metabolism which preserves the tissue rather than allowing swelling and disordered repair.
This is a slightly simplistic way of looking at it all, but is another reason why we ice swollen area.
Edit: as u/epote has pointed out the leap to brain cooling in trauma is probably one that shouldn’t have been made here. Apologies for the somewhat misleading info. Left for context but consider this edit a redaction of that statement!
Contrary to what most people are saying on here, ice does not reduce swelling. It does reduce pain and has other therapeutic and helpful healing properties but there is no clinical evidence to support the reduction of swelling. Also swelling is not an increase of blood flow to the area but rather fluid leaking out of blood vessels into the surrounding tissue.
Source: article on the topic that sites multiple medical journals as sources https://www.clinicaledge.co/blog/5-minute-physio-tip-crushing-the-myths-of-ice-application-is-ice-useful-for-acute-injuries-and-does-it-reduce-swelling
Does putting ice on a laceration also reduce bleed out? I read that in the Dresden novel where a woman gets hit by a car while water skiing.
It doesn’t.
If ice reduced blood flow why is your skin red and puffy after application? Wouldn’t it be grey and contracted?
Lymphatics 101
There is extra cellular fluid in the interstitial space between cells. That fluid finds a precollector (think microscopic toilet bowl) and dumps in. The fluid passes through a one way valve and becomes lymph. Lymph is peristaltically moved through vessels by tiny muscles called lymphangions and eventually finds its way back to the cardiovascular system at the brachialcephalic branch.
When ice is applied, the cold causes the lymphatic vessel walls to become permeable and the lymphatic fluid flows back into the extra cellular space slowing down the healing process because it has to start over. Ice can actually increase overall swelling because of this as it creates additional work for the lymphatic system.
Check out books from Gary Reinl and lymphatic physician Dr. Bruno Chikly.
Broke my damn leg last week. I as well am curious as to why I must put this icing on my leg.
ELI5: You have muscle cells in your blood vessels that make them get bigger or smaller. When you’re hurt, they get bigger to allow more help to get there, like how cars get out of the way of ambulances and fire trucks with their sirens on. When you put ice on it, the vessels get smaller because they know sending blood there will make it cold, and that will make your whole body cold.
ELI15: Swelling is part of the wound healing process. When damaged is detected by circulating white blood cells, they release chemicals that increase blood flow to the area so more white blood cells can get there and so oxygen and nutrients continue to reach nearby cells. The increase is caused by vasodilation – blood vessels (vaso) becoming larger in diameter (dilation). Nerve cells detecting cold, like when you put ice on a wound, send out the opposite signal, causing vasoconstriction.
A lot of the responses here reference vasoconstriction as the reason why ice reduces swelling, but that doesn’t really explain how fluid returns to vasculature, it just prevents further swelling. There’s little evidence that shows ice actually has an effect on edema:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5300735/
It does slow nerve conduction, so it kinda feels like it hurts less. It also does slow cell metabolism, but that also doesn’t promote ecf return to vasculature.
There is some partially correct answers in this thread, but most of them seem to be taking information from experience or poor sources. I’ll try to bring it together a bit. I’m a physical therapist and athletic trainer, for reference.
After an injury, cells are damaged. Our body has several responses to damaged cells, all in an effort to return them to their prior state. The primary response is INFLAMMATION. Inflammation and swelling are often used interchangeably, but not necessarily the same thing. Inflammation is a biochemical process stated by the damage to healthy cells, and this chemical process creates a lot of heat, as well as being an irritant to surrounding healthy tissue and also causes increased nerve sensitivity. There is also an increase in fluid collection at the area of injury, which is what most people think of as swelling.
The ice part of RICE (rest, ice, compression, elevation) helps to slow the chemical process (to prevent more damage to other surrounding tissue) while the compression and elevation helps to decrease the EDEMA. Edema is another word for swelling, but it can be present without an acute inflammatory response. People with lymphatic deficiency tend to have lymphedema, which is a collection of fluid in the arms and legs that the body can’t process which leads to them looking swollen. Icing won’t help at all with lymphedema, but compression garments can be effective in management.
So, icing is helpful to decrease collateral damage to nearby cells after acute injury and will reduce inflammation, but it won’t do anything for fluid accumulation.
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