What causes the warm feeling/muscle relaxation when you apply it? Does it actually cause muscle relaxation?
It’s what we call a “counter irritant”. It annoys the nerves which transmit the signal your brain reads as “heat”. Those nerves fire faster than the nerves which signal “pain”. Since they get there first, the “heat” signal temporarily uses up the neurotransmitter that passes the signal along, and the “pain” message can’t get through.
Kinda. Sorta. In layspeak.
The active ingredients are menthol and camphor. There are some other herbal things in there. There’s clove oil which at higher doses does actually numb, not just cause heat impulses, but it’s not really strong enough in the formula to do more than make it smell exotic. Cajeput and Cassia (more commonly called cinnamon, in the US) and Mint round out the formula according to the energetics of Traditional Chinese Medicine and make it smell nice and herbal mediciney.
It doesn’t directly cause muscles to relax. Rubbing it in to apply it does, and freedom from pain can help people stop “guarding” or tensing up to avoid more pain, allowing the muscles to relax.
Thank you. Do you happen to have any cites? Not that I disbelieve you, I have to convince someone else, and it’d be easier with a different source.
Also, I was in a bit of a hurry when I put up the OP, my curiosity also extends to other (non steroidal) topical muscular pain relief preparations. Do they work in the same way?
Capsaicin works the same way - Capsaicin and camphor/menthol are the most common counter irritant topicals. Sometimes eucalyptus and wintergreen are used, but usually in combination with capsaicin or camphor, not on their own. Turpentine rubs were a classic counter-irritant, but not really used today. Stinging nettles, belladonna, mustard plasters…all counter irritants used historically and sometimes by trained herbalists today, of varying safety. I wouldn’t play with those without training.
Some creams, like some versions of Aspercreme and Ben-Gay, contain salicylates, essentially aspirin, and those are purported to work differently, by blocking the production of prostaglandin, a chemical we need to feel pain. Same way aspirin and NSAIDS work internally, only they claim it’s absorbed through the skin. The FDA is unimpressed, and I don’t believe they’re allowed to make that as an actual health claim on the label. Most of these salicylate containing creams also contain camphor or menthol, so they’re working as counter irritants as well as, maybe, NSAIDS.
Narcotic creams and patches, of course, work like narcotics, blocking pain receptors in a more direct (chemical) fashion. You won’t find those over the counter, and you shouldn’t find them at your local herbalist’s, either.
The counter-irritant theory I spoke of is called the “gate control theory”. Here’s a nice crunchy granola cite: http://suite101.com/article/what-is-counter-irritation-a219715
Here’s a more scientific look, with schematics: Gate Control Theory of Pain | HowStuffWorks
Here’s one for nurses: Gate Control Theory
Or, if it helps, you can show your friend this thread and let him/her know that I’m a massage therapist, herbalist trained in Traditional Chinese Medicine and a Registered Nurse. 
Some these substances contain isopropyl alcohol which is also a counter irritant, and has a mild anesthetic effect.
Huh. Now that one, I did not know. 
(And not to be bratty, but can we have a source? If I can cite it, I can use it, but my nursing supervisor is a stickler for that “evidence based medicine” thing.)
Thank you! The dope’s always a great place to have questions answered by knowledgeable folk.
My quick search found wikipedia as a source for the effects, but under rubbing alcoholwhich can be a mix of isopropyl and ethanol. Perhaps only ethanol is providing that affect, but isopropyl was once recommended to me by a doctor for pain following an injury (to be used with caution). Some stuff I have call Therapeutic Ice, similar to Mineral Ice, lists isopropyl as an ingredient, but under inactive ingredients. I’ve seen it listed as an ingredient in Mineral Ice but I don’t recall if it seperated active and inactive ingredients. So at the moment I’m not clear on this myself.
That’s how it works against, say, insect bites, but Asians use it to combat colds and fevers as well. Westerners use Vick Vapor Rub (also camphor and menthol) for the same reasons. How does that work?
A related question that I don’t think was answered above: Do any of those ingredients even penetrate to tissue beneath the skin? I didn’t think so, but I couldn’t find anything to confirm it.
I am interested in knowing the answer to this as well, although WhyNot’s response seems to indicate that they don’t.
Voltaren (diclofenac) seems to work as a prostaglandin blocker as well. I was prescribed a cream by the doctor, so I think this is medically accepted.
It doesn’t.
Interesting that it excites the heat receptors, as it feels like it does the exact opposite. It always feels cold.
I’m also pretty sure that same counter irritant effect can help you not feel the irritation of a cold. It definitely feels like the same cooling sensation I described above, but in my sinuses.
I do not know if any of this stuff actually, physically, penetrates the skin. That’s a question for a pharmacist, who knows more stuff about size of molecules and permeability of the epi/dermis. Certainly some stuff penetrates the skin: testosterone gel, nicotine and fentanyl, for example. And some stuff penetrates only the top layers of the epidermis, but doesn’t go down below the dermis: “anti-aging” skin creme, self tanning lotion, henna dye molecules. And some stuff doesn’t penetrate anything at all: makeup, skin masks, soap…
I find that when I have a cold, *anything * new makes it feel better for a few minutes. Rub my chest with smelly stuff? Ahhh…that feels better. Bring me a cup of tea? Ahhh…that feels better. Ooh, a new book? Ahhh…that feels better. A DVD and a comfy couch? Ahhh…
It doesn’t always have to be medicinal to be therapeutic.
Vicks on the chest is one of those “if your mom did it for you when you were little, it tends to work great, if you try it for the first time as an adult, you think ‘what a smelly mess’ and that’s about it.”
Though this study does imply that it does something: http://pediatrics.aappublications.org/content/early/2010/11/08/peds.2010-1601.abstract
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