Therapeutic heating — “thermotherapy” for therapy geeks, the opposite of its trendier cousin, cryotherapy — is more useful than most people realize, mainly because muscleis a source of more and worse pain than most people realize, and muscle pain seems to respond well to heat. Muscle pain caused by over-exertion, muscle cramps and spams, and especially trigger points (muscle “knots”) are all common and sometimes severe, but often mistaken for other kinds of problems.

This therapeutic staple has mostly been ignored by science: its benefits are far from proven, and obviously it’s no miracle cure.1 Nevertheless, it’s probably doing more than “just” relieving symptoms. (Not that we should knock symptom relief.2) Everyone should understand heating the same way everyone knows how to put on a bandaid: it is a cheap, drugless way of taking the edge off an amazing array of common painful problems, especially neck and back pain, and maybe more.

Quick safety notes: you should rarely ice low back pain, but heating pads are safe during pregnancy(just avoid directly heating the belly). If you have freshly damaged tissue — obvious trauma, with redness and swelling — you should probably mosey on over to the icing article instead. Not sure when to use ice or heat? Start with this summary: The Great Ice vs. Heat Confusion Debacle.

What heat is for: mostly non-inflammatory body pain

Heat is primarily for relaxation, comfort, and reassurance, and taking the edge off of several kinds of body pain, mostly duller and persistent pains associated with stiffness, cramping, and/or sensitivity, which can be loosely categorized:

1. Acute soreness from over-exertion: the pain you get after the first ski trip of the season. (Interestingly, not only is heat likely helpful for this kind of pain, it’s almost the only thing that is! More about this below.)
2. Stiffness and pain in specific areas related to osteoarthritis, muscle “knots” or trigger points, and most kinds of cramping/spasm3 (menstrual, neuropathic, restless leg syndrome, for example, or even just stiffness from postural stress). But not, of course, cramps from heat exhaustion!
3. “Hurts all over” pain and sensitivity. There are many kinds, but primarily: fibromyalgia, the rheumatic diseases, drug side effects,4 vitamin D deficiency, and sleep deprivation.

There are many other kinds of pain, of course, but these are the ones most likely to benefit from heat. No one with appendicitis or a 2^nd degree burn wants a nice hot water bottle.

How does heat therapy work?

The next several sections explore different mechanisms and details of how heating might be helpful to people in pain:

• Heat is reassuring, and reassurance is analgesic. (This is applied neurology, not just a psychological effect.)
• Heat can penetrate a few centimetres into tissue, and cells and biochemistry speed up when the tissue temperature rises, which might have therapeutic implications. For instance …
• Heat may have an effect on the common painful phenomenon known as “trigger points.”
• Heat may help soreness after exercise.
• Tiger Balm and similar products are “spicy” not warm, but they might tinker usefully with sensation: a neurological distraction.