How would you define an allergen?

An allergen is defined as a substance that can trigger an allergic reaction in individuals who are sensitive to it. This reaction occurs when the immune system mistakenly identifies a normally harmless substance as a threat, leading to a range of symptoms that can affect the skin, respiratory system, gastrointestinal tract, and more. Common allergens include certain foods like peanuts, tree nuts, fish, shellfish, eggs, milk, soy, and wheat, as well as substances like pollen, dust mites, and pet dander.

The other options describe different concepts related to food safety but are not accurate representations of what an allergen is. Incorrectly stored food pertains to food safety practices to prevent spoilage or contamination, harmful bacteria refer to pathogens that can cause foodborne illnesses, and methods of preserving food relate to techniques used to extend the shelf life of food products. None of these reflect the definition of an allergen, making the first option the most accurate representation.