# Question about thermal heat patches **URL:** \ **Category:** Factual Questions\ **Created:** [September 14, 2003, 1:28am UTC](https://boards.straightdope.com/t/question-about-thermal-heat-patches/201483 "2003-09-14T01:28:22Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Guinastasia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/guinastasia/32/5751_2.png) [@Guinastasia](https://boards.straightdope.com/u/Guinastasia)\ **Post date:** [September 14, 2003, 1:28am UTC](https://boards.straightdope.com/t/question-about-thermal-heat-patches/201483/1 "2003-09-14T01:28:22Z")
All right, I was using one of those “thermal heat patches” to help with my cramps. On the package, it says you can discard when cool, and as it wasn’t quite cool, I wet it. Curious as to what was inside, I cut it, and there was this black dirt like substance. I threw it away and washed my hands. Now, I just read the package again and it says: > [@](#): > > Each heat patch contains iron, which can be harmful if ingested… Do not puncture or allow contents to come in contact with eyes or skin. If contact occurs, rinse right away with water. This product has the potential to cause skin irritations or burns. Am I going to get some hideous rash? Or worse-iron poisoning? Please help this stupid hypochondriac! 😉 ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [September 14, 2003, 1:55am UTC](https://boards.straightdope.com/t/question-about-thermal-heat-patches/201483/2 "2003-09-14T01:55:44Z")
The black dirtlike stuff was very finely divided iron filings. They rust (oxidize) when exposed to air and give off heat. If you had opened the package _before_ the iron was mostly oxidized, you could have gotten the stuff on your skin, where it would give off heat, and possibly burn you. Once the iron is oxidized, its no more dangerous than the scrapings from a rusty tailpipe. It can be pretty messy though !