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. The auto-injector is designed for easy use, allowing individuals to administer the medication themselves or have someone assist them during an emergency. It is crucial for people with known severe allergies to carry an epinephrine auto-injector at all times and to seek immediate medical attention after its use.