An allergen is any molecule that is capable of eliciting an allergic response. Molecular components of milk, latex, shellfish, and peanuts are all examples of strong allergens that can trigger a life-threatening immune response known as anaphylaxis.

Triggering of allergic responses

The allergic response is triggered when myelocyte class immune cells like neutrophils, basophil, and mast cells are triggered to release large amounts of chemotactic and vasodilatory signaling factors like histamine. Released systemically in large enough quantities, these chemicals can cause critical blood pressure drop and heart failure due to the volume of blood liquid lost to tissues due to inflammatory swelling.