Ice

What is it? Frozen water.

Does it work? It very much depends on the source of your pain, and even then, like with heat, the relief is only temporary. According to this article, the theory is that it works through numbing your nerve endings and constricting your capillaries. All of which is good news if what you have is inflammation or pain where these actions help. Unfortunately, according to this article by the same author, if your problems are due to knots or spasms in your muscles, then icing is likely to make you worse, as it's likely to cause (more) spasms in your muscles. In other word, it'll make your muscles tense up. That's why I've never even tried it, so can't speak from personal experience. My muscles are tense enough already and winter makes me worse, so I've never even wanted to ice. On the other hand, a friend of mine with neuropathy finds cold water and ice very useful for reducing his pain - it works better for him than the meds he takes for it.

Who does it work for? Ice may work for people with inflammation, and is therefore frequently recommended for inflammation, sprains and strains although there is little empirical evidence to back the recommendation up. In fact, people with strains and sprains are specifically told to use ice and avoid heat (which may or may not in the end prove to be correct advice, but is definitely the current NHS recommendation for sprains and strains). However, the articles I quoted above argue that chronic muscle pain probably isn't caused by inflammation (see the next section). For people with muscle-based pain, the articles above recommend ice only for hot, puffy areas of your body where the pain was caused by recent major exertion and not for chronic muscle pain. For neuropathic pain, I found this article recommending trying ice if heat doesn't work, and particularly if you get oedema (fluid build-up) in your hands or feet, as it may help reduce the swelling. A friend of mine finds using ice packs on his neuropathic (foot and leg) pain very helpful, and also putting his feet in cold water, but notes that it is only effective while he is doing it and makes it hard to do much at the same time.
Some people also say ice packs help for the pain of gout.
Also, another theory suggests that the pain you're treating should ideally be near the surface of the skin and/or in your neck or one of your extremities, as most people's bodies are extremely good at controlling their own temperature and therefore the effects of ice aren't likely to penetrate very deeply. On the other, hand, I'm not going to rule out a distraction or placebo effect, or even an effect that science can't yet account for, so if you fancy ice and there's no reason not to use it, then there's little harm in trying. 
On a side note, from personal experience, I can also say that I find itchy skin (and in my case specifically eczema) can calm down to a level where it's not so insistent about being scratched if I press it against something cool like room-temperature metal (e.g. a cold radiator), although I've never tried ice, as the room temperature metal seems a better temperature to me (obviously, if you live somewhere hotter than the UK, and in particular hotter than human body temperature, you'd want something much cooler than room temperature metal, for instance a refrigerated cool pack).
 
Who doesn't it work for? Probably most people with chronic musculoskeletal pain, who are likely to be better off using heat. The guy who wrote the articles above (a qualified massage therapist who has spent a long time focusing on treating people with chronic muscle pain), reckons that inflammation is uncommon in chronic muscle pain, and that by the time pain becomes chronic, even if it started out as inflammation, it's no longer likely to be caused by inflammation once it reaches chronic proportions, even in things like shin splints, where the pain was initially caused by inflammation and your diagnosis remains the same after it becomes chronic. Instead, he thinks you're likely to be suffering from tissue degeneration or muscle knots. There's little evidence either for or against this approach, but taking a cautious approach to using ice for chronic musculoskeletal pain sounds a sensible approach to me. If you have musculoskeletal chronic pain and don't fancy the idea of ice, don't use it. If you do fancy the idea of ice, listen to your body. Apply it as he recommends and if your body says "ooh, no, stop that, this is worse", listen to it and stop that. If it says "ooh, this is nice, I really like this, more please", then listen to that too. The thing about ice is that unless you're stupid with it and give yourself an ice burn (or take an ice bath), the worst you're likely to do is make your body feel like it's been out on a winter's day (obviously you're not going to make your pain any better by doing this repeatedly, but once or twice isn't likely to have a long-term impact).
Also, 7 studies with 328 participants found no significant effect of hot or ice packs for rheumatoid arthritis, so it's probably pointless for that.
Also, don't use ice if you are allergic to it (e.g. you get hives from it), you have Raynaud's Phenomenon (another reason for me and many people with HMS not to use it), decreased circulation or desensitised areas (I think that means areas where you can't feel the cold, so wouldn't know if you'd applied it for too long).

Where can I get it? The freezer.
No seriously, your freezer. You can just use ice from your freezer, for instance wrapped in a tea towel or in a bag, or freeze yourself an ice cup. You can find instructions on how to make an ice cup and also instructions on how to use it here. If you find that useful, instead of using a polystyrene cup each time, you can buy your own commercial ice cup, such as this one or this one. You can also use gel packs or bean bags that you store in your freezer. You can find instructions on how to use them here. It's also possible to have an ice bath (i.e. run a cold bath and add ice), although that mainly seems aimed at people trying to avoid pain after exercise, and please also bear in mind that the same article describes ice baths as "torture", says they're not well studied and warns they can be dangerous because the shock of immersion can affect the heart, blood vessels and respiratory system and raise blood pressure and the heart rate, and the long-term effects are unclear. Other similar, but less tortuous options that may help include putting the area with pain in cold water or having a cold bath of shower (just cold, not filled with ice). No one seems to have studied this, so you'll have to decide for yourself if this helps you or not.


How much does it cost? If you have a freezer anyway, the only cost is for the container for freezing ice. Your freezer probably already came with an ice cube tray. Alternatively, these ice cube bags for £1 make a handy bag to stop the water dripping everywhere. Also, you can keep refreezing the same bag if you want (although you probably shouldn't consume the ice you've done that to). You can get 10 foam cups to make ice cups from for £1. The pro-tec ice-up is £20.99. I found the Cryocup available at £77.94 for 10! It doesn't seem widely available in the UK.

Is there a cheap or free version? There's no getting round the need for a freezer (unless you live somewhere that has freezing temperatures outdoors), but if you have that, then everything else is already pretty cheap (or free if your freezer came with ice cube trays).

Is there any evidence for it?  More information seems to have been gathered on ice for acute pain or post-exercise pain than for chronic pain. However, one low quality trial found that light ice massage and TENS were similarly effective in reducing chronic low back pain. A further two low quality non-randomised trials reported conflicting results on ice versus heat. One found no significant difference between hot packs and ice massage for back pain of mixed duration and the other found ice massage superior to hot packs for chronic low back pain (unfortunately, a non-randomised trial is only a small step up from anecdotal evidence, so this isn't ideal). I also found this small study on ice therapy for peripheral neuropathy on 33 participants. Unfortunately the way they wrote up the result left me unclear as to whether they thought it was successful ("the results of the study were negative, there was a decrease in pain intensity over time with both the ice massage and towel massage, suggesting that the intervention has some clinical benefit"). Anyhow, basically, the studies that have been done have been small and/or non-randomised and have had mixed results, so not great evidence, and the evidence that my friend says it works for him is strictly anecdotal evidence, so about the lowest quality evidence you can get, but doesn't rule out the possibility it might also work for you if you have the right sort of pain.

Are there any downsides? Yes. Because of its tendency to make muscles tense up, ice can make your pain worse if your pain is created or exacerbated by muscle tension, muscle spasms or muscle knots. Also, some people find applying ice unpleasant. If either of these applies to you, don't do it. There's no proven long-term benefit. The benefit, if any, is likely to be short-term and temporary (OK, given how little research there is on the subject, this could later be proven untrue, but for now the safer assumption is that it's only providing short term benefits, and if you're not getting those, then there's no point and you may even be making yourself worse). Also, an ice bath could be dangerous for people with heart, respiratory or high blood pressure problems (and is apparently also as deeply an unpleasant an experience as it sounds). Finally, even applying ice locally could give you frostbite or an ice burn if you do it for too long. However, according to this article, this sort of tissue damage doesn't occur until at least three minutes after you've gone numb, so providing you stop at roughly the time when your skin goes numb (and providing you have normal ability to sense heat and cold and numbness), you shouldn't experience a problem.

Are there any other upsides? This is drug-free, cheap method of reducing pain. It may also be good at reducing inflammation, current medical advice says it is, but empirical evidence has not yet been gathered.

Was it worth the money/effort? For me, no. I've never had the right type of pain or the will to try it, and also I have Raynaud's Phenomenon, so it's a bad idea for me. My friend with neuropathy says yes, it's totally worth it and one of the best forms of relief he has.

Do you have any experiences of using ice to treat chronic pain? What did it work (or not work) for? What method did you use?