The overall goal of our immune system is to protect the healthy cells of our body from invading pathogens, such as bacterial cells or viruses. It's to generate and maintain a state of homeostasis. Now, as with many things in life, our immune system is not a perfect system. And sometimes it does make mistakes. Sometimes the immune immune system incorrectly labels an otherwise non harmful foreign substance that enters our body as being harmful as pathogenic. And this elicits, it initiates a defensive response called an allergic reaction.