Chemicals Used in a Cold Pack

Applying ice to an injury is often one of the first steps to treat sprains, strains, muscle pulls and other common injuries. Cold therapy helps to constrict the blood vessels, reduce swelling and decrease inflammation. It can also numb the area to reduce pain. Using ice or a cold pack is also beneficial for managing flareups of chronic conditions such as arthritis, headaches and back pain. As an alternative to freezer packs which need to be stored in the freezer, instant ice packs are a popular choice because they are portable, can be stored at room temperature, and are easy to use. In addition to water, one of a few common ingredients are found in these instant cold packs.

Ice packs are good for injuries. (Image: Fuse/Fuse/Getty Images)

Ammonium Nitrate

Ammonium nitrate has traditionally been the most common chemical used in instant cold packs. This chemical is kept separate from the water inside the pack until the seal is broken -- which is accomplished by bending or squeezing. Next, this ammonium salt dissolves in water and leads to an endothermic reaction. This means the solution absorbs heat from its surroundings, and the temperature of the cold pack's fluid drops to any icy level. Calcium ammonium chloride, which works in the same manner, may also be the active ingredient in these instant cold packs.


Ammonium nitrate can be harmful to the body if it leaks from the cold pack and is swallowed, inhaled or comes in contact with the skin. In certain situations, ammonium nitrate is capable of exploding, and incurs additional shipping costs because it is considered a hazardous material. Given this, some companies use nontoxic urea in its place. Urea also initiates an endothermic reaction after mixing with water, in order to transform the pack to an icy temperature, ready for use in cold therapy.


As part of therapy to treat injury or improve symptoms, ice packs may be used several times daily for 10 to 20 minutes at a time. Longer application can cause a burn from the cold temperatures. Also, place a cloth between your skin and the ice pack to prevent burn. If any of the chemicals leak out and are exposed to the skin, inhaled or swallowed, check the package label to identify the chemicals used, and call your doctor right away or the poison control hotline for guidance.

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