Allergy is A PART of our immune system. Yes, you heard it right. Allergy is process by which our body sends an abnormal reaction to an external agent in the systems. The agent mentioned here refers to a particle that gets into the human body through the air/skin/water/food or any other pathway. These particles are called as Allergens. Allergens are classified under the large category of antigens. Antigens are can be defined as any particle, which upon getting into the body, sets an immune trigger from the immune system. A point to be noted is that an antigen/allergen is not necessarily a negative or a destructive substance. Most of the times, specifically in the case of an allergy, antigens are just normal food particles or matter, which our body, unfortunately, has an issue with.