# How do Thermacare patches work?

**URL:** <https://boards.straightdope.com/t/how-do-thermacare-patches-work/276593>\
**Category:** Factual Questions\
**Created:** [November 25, 2004, 3:27am UTC](https://boards.straightdope.com/t/how-do-thermacare-patches-work/276593 "2004-11-25T03:27:06Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\
**Post date:** [November 25, 2004, 3:27am UTC](https://boards.straightdope.com/t/how-do-thermacare-patches-work/276593/1 "2004-11-25T03:27:06Z")

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I’ve used these off and on for a year or so and they work great! I’d slept in a bad position and woke up with a horribly stiff neck and shoulders. I used one of the patches overnight and the next morning the pain was about 90% gone.

According to the instructions, they are “air activated”.

In the package, they are folded and in a foil packet until they are needed.

How do these things work?

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**Author:** ![CapnPitt](https://avatars.discourse-cdn.com/v4/letter/c/edb3f5/32.png) [@CapnPitt](https://boards.straightdope.com/u/CapnPitt)\
**Post date:** [November 25, 2004, 3:35am UTC](https://boards.straightdope.com/t/how-do-thermacare-patches-work/276593/2 "2004-11-25T03:35:16Z")

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Here’s what I know 'bout Thermacare (from a friend who works in powdered metals): the thermacare packs contain pellets of powdered (compressed) iron. Upon contact with the air, the iron oxidizes and heat is released as part of that chemical reaction.

Don’t know the science, but the friend who told me is an extremely reliable source. So I guess that’s something to think about until someone with some actual knowledge comes along.

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**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\
**Post date:** [November 27, 2004, 9:17pm UTC](https://boards.straightdope.com/t/how-do-thermacare-patches-work/276593/3 "2004-11-27T21:17:04Z")

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Bump.

The package does say it’s air activated.

Can anybody explain further?

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**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\
**Post date:** [November 27, 2004, 9:35pm UTC](https://boards.straightdope.com/t/how-do-thermacare-patches-work/276593/4 "2004-11-27T21:35:23Z")

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The Capn is correct  
[PDR Drug information for THERMACARE® OTC (Procter & Gamble) Therapeutic Heat Wraps  
with Air-Activated Heat Discs](http://www.drugs.com/PDR/ThermaCare_Heat_Wraps.html)

> [@](#):
>
> INGREDIENTS  
> Heat cells contain activated charcoal, iron powder, sodium chloride, sodium thiosulfate and water.

> [@](#):
>
> Designed to fit your lower back and thin enough to wear discreetly under your clothing, ThermaCare allowes you to move freely while delivering therapeutic heat to relax your tight back muscles. ThermaCare Lower Back HeatWraps provide temporary relief of minor muscular aches and pains associated with overexertion, strains, muscle tension and arthritis. ThermaCare Air-Activated HeatWraps contain natural heat generating ingredients (iron, charcoal, table salt and water) that heat up when exposed to oxygen in the air

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**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\
**Post date:** [November 27, 2004, 9:38pm UTC](https://boards.straightdope.com/t/how-do-thermacare-patches-work/276593/5 "2004-11-27T21:38:33Z")

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Thanks to both.

Simple chemistry and man, does it ever work!