An epinephrine auto-injector is a medical device used to treat severe allergic reactions, known as anaphylaxis. It contains a pre-measured dose of epinephrine, a hormone that quickly narrows blood vessels and opens airways in the lungs, helping to alleviate symptoms like difficulty breathing and swelling. These auto-injectors are designed for easy use, allowing individuals to self-administer the medication during an emergency. They are typically carried by people with known severe allergies to substances such as peanuts, tree nuts, or insect stings. Proper training on how to use an auto-injector is essential for effective treatment.