Heating pads, also known as heat patches, are a warming device that converts chemical energy into heat through an accelerated oxidation reaction in a galvanic cell. Their heating material is composed of a composite of iron powder, activated carbon, vermiculite, inorganic salts, and water. After removing the outer gelatin layer, it reacts with oxygen to release heat. Vermiculite acts as an insulating material, maintaining an average temperature of 52°C for 8-18 hours. Pregnant women and infants are among those who should avoid using this product.
This product was invented in Japan in the 1970s and generates heat autonomously without the need for fire, electricity, water, or any other form of energy. Large-scale production began in the Chinese market in 2006, and by 2008, the domestic annual output had reached 181 million patches. According to the light industry standard "Heating Patches" (QB/T 4903-2016), the maximum temperature of heating patches should not exceed 70°C, the average temperature should not be lower than 48°C, and the duration of heat generation must be clearly indicated on the product packaging. They should be applied to the outside of clothing, avoiding direct contact with the skin to prevent low-temperature burns; contact with temperatures near 60°C for more than 5 minutes can cause burns.
The heating principle of heating pads involves an iron oxidation reaction: iron powder reacts with oxygen and water to form ferrous hydroxide, which is ultimately converted into iron oxide and water. Vermiculite and activated carbon work together to disperse the iron powder, preventing rapid heating and skin burns. Clinical tests show that it can relieve joint pain and menstrual cramps. Experimental data shows that after wrapping a raw egg with a heating pad for 5 hours, the internal temperature can reach 67.3°C. This product is managed as an industrial daily necessity, and there are differences in quality control compared to hot compresses regulated as Class II medical devices. When used correctly, there is no carcinogenic risk, but burns must be prevented.