Is an allergen a substance of allergic reaction in individual?

An allergen is a substance that can cause an allergic reaction in individuals who are allergic to it. Allergens can be found in a variety of sources, including foods, pollens, dust mites, pet dander, and insect stings. When an allergen is introduced into the body of a person who is allergic to it, the body's immune system overreacts, producing antibodies that target the allergen. This reaction can cause a variety of symptoms, including sneezing, coughing, watery eyes, runny nose, hives, and shortness of breath. In severe cases, an allergic reaction can be life-threatening.