What is an allergy?

An allergy is accurately defined as an immune response to a substance that is typically harmless to most individuals. When a person has an allergy, their immune system mistakenly identifies a harmless substance—such as pollen, dust mites, or certain foods—as a threat. This response can lead to a range of symptoms that can vary in severity, from mild reactions like rashes or sneezing to more severe reactions such as anaphylaxis.

This definition emphasizes the immune system's role in allergies and clarifies that these responses can occur with a variety of substances, not just medications. Other choices do not capture the full scope of what an allergy entails. For instance, a response to medications is just one aspect of allergies, not the entirety of the concept. Furthermore, describing an allergy as an airborne illness affecting the respiratory system or as a symptom of a cold or flu misrepresents the underlying mechanism of allergies and their symptoms, which can affect various systems in the body and are not limited to respiratory concerns.