Q.A person shows strong unusual hypersensitive reactions when exposed to certain substances present in the air. Identify the condition. Name the cells responsible for such reactions. What precaution should be taken to avoid such reactions.

The condition is allergy, specifically a type I hypersensitivity reaction. The cells responsible are mast cells, which release histamine and other inflammatory chemicals when triggered by allergens like pollen or dust in the air.

To avoid such reactions, the person should identify and avoid exposure to the specific allergen — for example, staying indoors during high pollen seasons, using air purifiers, or wearing a mask. In severe cases, doctors may prescribe antihistamines or desensiti …

When a person develops strong, unusual hypersensitive reactions to substances that are normally harmless — like pollen, dust, or animal dander in the air — the condition is called allergy. The NCERT textbook describes allergy as an exaggerated or hypersensitive response of the immune system to certain antigens present in the environment. These antigens, which trigger the reaction, are known as allergens. Common examples include pollen grains, dust mites, mould spores, and even certain foods or drugs.

The cells primarily responsible for these allergic reactions are mast cells. When an allergen enters the body for the first time, it stimulates the immune system to produce a special type of antibody called IgE (immunoglobulin E). These IgE antibodies attach themselves to the surface of mast cells, which are abundant in tissues like the respiratory tract, skin, and digestive tract. Upon subsequent exposure to the same allergen, the allergen binds to these IgE antibodies on the mast cells, causing the mast cells to release powerful chemical mediators — most notably histamine. Histamine is the key substance that causes the symptoms we associate with allergies: sneezing, runny nose, watery eyes, itching, and in severe cases, difficulty in breathing.

The severity of allergic reactions can vary widely. In some individuals, the reaction may be mild and localised, but in others — especially those with a family history of allergies — it can be severe and even life-threatening, leading to a condition called anaphylactic shock. This is a medical emergency where blood pressure drops dangerously and airways constrict. …

Method: Identify by Antibody Class and Cell Type, Not Symptom Alone

Use an immunology decision-tree: identify the antibody class involved first, and the condition and responsible cell follow directly.

Step 1: Note the trigger — an airborne substance, normally harmless, provokes an exaggerated reaction. This pattern (harmless antigen + exaggerated reaction) is diagnostic of hypersensitivity, specifically allergy (Type I hypersensitivity).

Step 2: Identify the antibody class involved

Type I hypersensitivity is specifically the IgE-mediated type — on first exposure to the allergen, the body produces allergen-specific IgE antibodies (as opposed to IgG/IgM, which dominate normal infection responses).

Step 3: Identify where that antibody sits

IgE binds to the surface of mast cells (abundant in the respiratory tract, skin, and gut) rather than circulating freely.

Step 4: Identify the trigger event and released mediator …