Applying ice to an injury is often one of the first steps of an overall treatment plan for sprains, strains, muscle pulls and other common injuries. Cold therapy helps to constrict the blood vessels, reducing swelling and inflammation. It can also numb the area to reduce pain. Cold therapy is beneficial for managing flareups of chronic conditions such as arthritis, headaches and back pain. Instant ice packs are a popular choice when applying cold therapy because they can be transported and are easy to use.
Ammonium Nitrate or Urea
Ammonium nitrate is the most common chemical used in cold packs. This chemical works by first dissolving in water, which makes it capable of absorbing heat. The ammonium nitrate and the water found in an instant cold pack are kept separate until the pack is activated, usually by striking or bending it to break the inside seal. As the two mix, the temperature of the cold pack drops. However, ammonium nitrate is toxic and can be harmful to the body if it leaks from the cold pack. Given this, some companies use urea in its place, which is non-toxic.
Ammonium Chloride and Potassium Nitrate
While not as common, ammonium chloride and potassium nitrate can also both be used in instant cold packs. These two chemicals cause the temperature of water to drop quickly as they dissolve in the water.
It is possible to make a gel-like cold pack at home by mixing one part rubbing alcohol with two to three parts water in a plastic bag. The bag can be kept in the freezer. The water will freeze to make the pack cold but the rubbing alcohol will not freeze. This will make the ice pack flexible and able to conform to the shape of the body. The higher the ratio of alcohol, the less solid the pack will be.