Q.Define an allergen and give one common example.

An allergen is a substance — usually otherwise harmless to most people — that the immune system of a susceptible individual mistakenly identifies as dangerous, triggering an allergic reaction. Common allergens include house dust and dust mites, pollen grains from certain plants, animal dander, particular foods (such as peanuts or shellfish), and some medicines. In a susceptible person, exposure to the allergen leads to IgE antibody production and, on renewed exposure, the release of histamine from mast cells, produci …

Define the term and immediately support it with a concrete, familiar example (dust or …

Do not describe an allergen as inherently 'dangerous' — the key point is that it is normally harmless; the problem lies in the immune sy …