One of the first remedies recommended to relieve pain and swelling from a minor injury is often an ice pack. Portable medical ice packs contain chemicals that react with each other to cool the ice pack to therapeutic temperatures. These ingredients are common, relatively inexpensive and create a highly effective cold pack. Other types of medical ice packs can be made at home and stored in the freezer.
How chemical ice packs are made
Most chemical ice packs for medical use consist of a heavy duty plastic bag filled with water. Inside this bag, separated from the water by a plastic membrane or glass vial, is a smaller container of a chemical like ammonium nitrate. When the ice pack is squeezed or "cracked" per manufacturer instructions, the ammonium nitrate is allowed to mix with the water. The water and the ammonium nitrate then undergo an endothermic reaction. This type of reaction cools things down, and the ice pack becomes cold. These chemical ice packs can only be used once.
Other ingredients in medical ice packs
Some ice packs contain ammonium chloride or potassium nitrate rather than ammonium nitrate. These ice packs are constructed in the same way as those containing ammonium nitrate. The chemicals each react with the water more quickly to produce a colder ice pack. However, these ice packs don't last as long as those containing ammonium nitrate. Use this type of ice pack with caution, following the manufacturer's instructions, because the extremely cold temperature generated can damage skin.
The chemicals used in medical ice packs are somewhat toxic. Ammonia is poisonous to humans if ingested, and if placed directly on the skin it can cause chemical burns. Also, these chemicals can be toxic to aquatic life forms. Therefore, it is important to dispose of medical ice packs properly and to avoid puncturing the outer pouch of the ice pack.
Homemade medical ice pack
A simple ice pack can be made at home and stored in the freezer for multiple uses. Water and isopropyl alcohol can be mixed and then placed in a double zipper-style freezer bag. The isopropyl alcohol helps to keep the ice pack from freezing solid, so it remains pliable and easy to apply to the skin. A ratio of about 1/3 alcohol to 2/3 water will make a slushy and pliable ice pack.
Nontoxic ice packs
Some people prefer a nontoxic alternative to the chemical ice packs containing ammonium nitrate and similar chemicals. These are not as portable as chemical ice packs because they need to be stored in the freezer, but a bag of frozen peas, a bag of ice wrapped in a towel, or a sanitary towel or nappy soaked in water and frozen can all make good ice packs in a pinch.