Should I put a heat pack or a cold pack on an injury?
Applying hot or cold to an area of pain is an age old remedy, but which is the right thing to do? Well, typically the short answer is ‘it depends’, both can be effective and both can make the situation worse. So how do you tell which to use at any given time? To understand this you need to have a basic understanding of the process of the inflammatory process.
The inflammatory process, or inflammation is the body’s response to injury or infection, it is how the body gets rid of threats, cleans up any damaged area and then rebuilds tissue to restore normal function. There are 2 stages to the process;
This happens very quickly after an injury, and is characterised by an increase in blood flow to the injured area (making it red), a dilation of the blood vessels (making it swell), and the arrival of various chemicals that increase sensitivity to pain (making it painful). This stage typically lasts for up to 3 days and pain tends to be more sharp and burning. In this stage the body is clearing up damaged tissues and getting rid of debris.
This stage is more concerned with the rebuilding of damaged tissue, and (depending on the severity of the injury) can last for anything from a few days up to several months. Tissue repair requires the deposit of a lot of dense connective tissue which forms a fibrous mesh of tissue to avoid the area being vulnerable to movement (proliferation), over time the movement in the area produces more organised tissues (remodelling) that looks more like the tissue pre injury (1). Due to the rebuilding of the tissues the injured area will feel stiff but less sore, due to the lack of inflammatory chemicals during this time.
How does cold/ice affect pain and healing?
When our bodies are exposed to cold temperatures several things happen to allow us to adjust. One of these things in vasoconstriction, the blood vessels close to the surface of the body constrict to reduce the blood flow to the surface to stop us losing heat, this is why people who are cold look pale. As we mentioned earlier, acute inflammation is characterised by vasodilation where the blood flow, along with its pain sensitising chemicals, is increased to the area of damage. As you have probably now worked out putting a cold pack on an area that is acutely inflamed will therefore reduce the presence of the painful chemicals in the injured area, resulting in a reduction of pain. This is why most very recent injuries can be made less painful by the application of an ice pack, anti-inflammatory medications also work by reducing these chemicals. The acute stage of the inflammatory process is a vital stage of healing, so does icing an injury slow down the healing process? The answer is predictably yes, as it reduces the body’s response, however research shows that short term icing of an injury for pain relief has no impact on eventual outcomes (2).
So, ice is good for pain relief of ‘fresh’ injuries, especially those that have the signs of inflammation such as swelling, redness and sharp pain. Simple methods such as using ice cubes or frozen peas wrapped in a barrier such as a tea towel are fine. As a vague rule, when you’re numb you’re done (3)!
When shouldn’t you use ice?
When there is a break in the skin, this will slow the body’s attempt to fight infection, or when there is generalised muscle pain such as when you have done too much in the garden or over trained (this is generalised muscle pain and will be worsened by icing it).
How does heat affect pain and healing?
Heat can affect pain levels when there is no inflammation present, and when the pain is generally muscular. As we know, heat will vasodilate an area and if that area is inflamed then that will increase pain, however, if there is no acute inflammation present then increasing the blood flow to an area will speed up recovery from exertion. So if you have stiffness or fatigue like pain from doing too much then the soreness is from a build-up of lactic acid, by applying heat you will increase the blood flow therefore speeding up the transport of lactic acid out of the tissues. Heat also increases the flexibility of connective tissue (laid down in the proliferation/remodelling phase of repair) so the area will feel less stiff. Heat and cold will both reduce pain if used correctly, however heat can also increase the speed of recovery of the affected tissues (1).
So heat is good for muscular stiffness from over exertion, and again, simple methods are very effective, such as hot water bottles or a hot bath (3).
When not to use heat
When here is visible swelling, redness or the injury is very recent as you will likely make the pain worse.
So, the next time you are struggling with pain or inury, if you want to try to control the pain before you are able to get some help you can apply these techniques!
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1 Brukner, P. and Khan, K. (2007). Clinical Sports Medicine (3rd Ed). McGraw Hill, Sydney.
2 – Collins NC. (2008). Is ice right? Does cryotherapy improve outcome for acute soft tissue injury? Emerg Med J. Feb;25(2):65–8.
3 – Carnes, M, & Vizniak, N. (2011). Conditions Manual. Professional Health Systems, Canada.