Both heat and cold can help reduce pain through the gate-control theory of pain. That doesn’t mean you should use whichever one you like better. The timing is critical. Beyond timing, each one has advantages and disadvantages that need to be understood to make an informed decision.
Here’s the short answer we give to patients at BioMechanics:
Use cold for sharp/stabbing pain or a new/swollen/inflamed injury
Use heat for long term pain
DISCLAIMER: Ice and heat are not substitutes for a medical evaluation and treatment.
When used properly, heat relieves pain and helps your body relax or loosen up.
How Heat Works
Heat has 2 main effects:
More Blood Flow
Blood vessels react to heat by relaxing and letting more blood pass through in a process called vasodilation. Heated tissues have more access to oxygen and nutrients (the building blocks for repair in your body). Heated tissues can also eliminate carbon dioxide and metabolic waste more easily. The increase in blood flow is effective in relaxing tight muscles because it breaks the pain cycle:
muscle spasm > pain and reduced blood flow > more muscle spasm
Makes things softer
Remember basic science from grade school? When you add enough heat, things change from solid to liquid (and eventually gas). Heated tissues in your body are softer, more elastic, and more flexible.
That sounds great right? Most people think so. Heating pads and microwave hot packs are the most commonly bought products for home use. Well then, why don’t we recommend heat for everybody in every situation? One reason is that the effect of heat therapy is gone only a few minutes after you remove the heat. There are also a lot of times where it can make things worse!
When to Avoid Heat Therapy
Heat can be dangerous. There are people who should never use heat. Most of the time, the problem is that heat is used in the wrong situations. Let’s look at when to avoid heat.
You should never use heat if:
- You have poor circulation – The area can become so hot that you are cooking the cells in your body
- You have nerve damage in the area (numbness) – same as above
- You have a bleeding disorder or are on prescription blood thinners – a small bleed could get worse.
The bottom line is if you have any problems with your nerves or blood vessels, consult a healthcare professional before using heat.
Situations where heat should be avoided:
- You have a new injury or recently flared-up and old injury (48 hours)
- You have sharp or stabbing pain
- You just had a hard workout or finished doing a lot of manual work (yard work, lifting boxes)
All of the above point to the early stages of an inflammatory response. Inflammation brings pain. It’s your body’s way of saying you shouldn’t use this part for a while.
heat = increased blood flow = increased swelling = increased pain
Adding heat in these situations will give you more pain and a significantly longer healing time. People often don’t notice that heat is making their problem worse.
The Heat Trap
Add heat to an inflammed area and it is usually soothing (temporarily). It takes hours for the extra swelling to do it’s thing and release more pain causing chemicals. What do you do a couple of ours later when it hurts even worse? You thinking to yourself “it felt better with heat last time” and put heat on the area again. Don’t do it. Don’t double down on heat when your problem feels worse a couple of hours later. You’ll be taking a short term problem into a longer recovery.
When to Use Heat Therapy
Heat is best for treating chronic pain. Chronic pain (>3 months) is typically described as dull, achy, tight and stiff. If you suffer from an ongoing injury you can apply heat before exercising to loosen the injured body part..
Limitations of Heat Therapy
Local heat (heating pad, hot water bottle) doesn’t penetrate deeply into the body – only about a centimeter or 1/3 of an inch.
Systemic heat (sauna, hot tub) raises the temperature of your whole body a few degrees. This might be great for your old knee injury but bad for the shoulder you strained yesterday.
Deep Local Heat (therapeutic ultrasound) penetrates deep into the body and heats only the intended area. Unfortunately, most people don’t have an ultrasound machine so you would have to head over to your local sports rehabilitation and chiropractic place.
Ice is numbing. That’s great because things that are numb can’t hurt (as much). Ice is used when the injury is recent, red, inflamed, or when pain is sharp or stabbing. Cold therapy penetrate deeper into your body than heat but still only affects tissues less than 3cm or 1 inch from the surface of your skin.
How Cold Therapy Works
The cold narrows blood vessels and slows down blood flow. It controls the bleeding and swelling related to a new injury. Ice also slows the ability of nerves to carry pain signals to the brain.
When cold therapy is applied properly you should feel the area go through 4 stages abbreviated as CBAN:
Cold > Buring > Aching > Numbness
That doesn’t sound as nice as the soothing effect of heat but the “numbness” stage is great and lasts longer than the soothing effect of heat.
When to Avoid Cold Therapy
Cold can be dangerous too. There are people who should never use cold. Let’s look at when to avoid cold:
You should never use cold if:
- You have poor circulation – The area can become so cold that you freeze the your skin (frostbite)
- You have nerve damage in the area (numbness) – same as above
Unlike heat, you can continue to use ice even if you have a blood clotting disorder or if you are on blood thinners. To be safe, if you have any problems with your nerves or blood vessels please consult a healthcare professional before using cold therapy.
When to Use Cold Therapy
- New injury – As the table above shows, using ice in the 1st 24 hours following an injury can help your injury heal much more quickly
- After exercise – Cold treatment can reduce post-exercise inflammation
- Cold therapy can sometimes also help relieve pain in chronic injuries
Tips for Applying Cold
There are two common mistakes I see people make with ice. Don’t pull the ice pack out of the freezer and slap it straight onto your skin and don’t leave the ice on for too long. To get the most out of ice follow these tips:
Never use ice for more than 20 minutes at a time
Leave ice on for longer and at best you will activate the Hunting Response and at worst expose yourself to mild frostbite.
Tip for Ice Packs
I recommend 15/45 – 15 minutes on, 45 minutes off and repeat as needed.
Always wrap ice packs in a towel
You need to be able to tolerate the cold through the stages of CBAN. When you place the ice pack directly on your skin the Cold, Burning, and Aching can be too intense. You are likely to quit icing before 10-15 minutes is up.
Tip for Towels
I recommend wetting a towel in warm water, ringing it out, placing the ice pack inside and immediately applying it to the injured area. Putting a warm towel on your skin is less shocking – you’ll avoid the tendency to tense up when something cold hits your body. Making it damp gives you the perfect balance between getting the are too cold (straight on skin) and not cold enough to be therapeutic (insulated by a thick dry towel).
Earlier Posts In This Series
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