Q.In the metropolitan cities of India, many children are suffering from allergy/asthma. What are the main causes of this problem. Give some symptoms of allergic reactions.

The sharp rise in allergy and asthma cases among children in metropolitan Indian cities is directly linked to the modern urban environment. The main cause is air pollution, particularly from vehicle exhaust and industrial emissions, which irritates the airways. A second major cause is indoor allergens like dust mites, cockroach droppings, and mould, which thrive in crowded, poorly ventilated homes. A third factor is the increased sensitivity of the immune system due to reduced exposure to infections in early childhood (the hygiene hypothesis), making it more likely to overreact to harmless substances.

Common symptoms of an allergic reaction include: …

To understand why so many children in big Indian cities suffer from allergies and asthma, we need to first grasp what an allergy actually is. An allergy is an exaggerated, hypersensitive response of the immune system to a normally harmless substance — called an allergen. Think of it as the body’s security system overreacting to a false alarm. In a child living in a crowded, polluted metropolis, this alarm is triggered far too often.

The main causes in metropolitan India are deeply tied to the urban environment. The most obvious culprit is air pollution. Vehicles, construction dust, and industrial emissions release fine particulate matter (PM2.5 and PM10) and gases like nitrogen dioxide. These pollutants don’t just irritate the airways; they actually damage the lining of the respiratory tract, making it more permeable and vulnerable. Once that protective barrier is weakened, common allergens like pollen, dust mites, and mould spores can penetrate more easily and trigger a stronger immune reaction. This is why a child in a city might develop asthma from levels of dust that a child in a cleaner area would simply sneeze at.

Another major factor is the indoor environment. Children in cities spend most of their time inside — in apartments, schools, and malls. These spaces often have poor cross-ventilation. Dust mites thrive in mattresses, pillows, and upholstered furniture. Cockroach droppings are a potent allergen. Mould grows in damp bathrooms and air-conditioning units. Add to this the use of synthetic carpets, air fresheners, and cleaning chemicals, and you have a concentrated cocktail of triggers that a child breathes in day after day.

Lifestyle changes also play a role. Diet and stress are also thought to influence allergic responses in city children, though this is general medical knowledge rather than something the NCERT chapter itself discusses. Less time spent playing outdoors, and less exposure to a diverse range of microbes, is sometimes linked to a more reactive immune system — an idea often called the “hygiene hypothesis,” a term the NCERT textbook does not use. …

Method: The Two-Phase Allergy Model, Applied to an Environmental Trigger List

Rather than listing "causes" and "symptoms" as two separate facts, run the actual allergy mechanism forward and show how environmental triggers plug into it.

Step 1: Phase 1 — sensitisation (silent, no symptoms). First exposure to an allergen (dust mite, pollen, mould spore, or a pollutant-damaged airway lining that lets these allergens penetrate more easily) causes the immune system to produce allergen-specific IgE antibodies, which coat mast cells.

Step 2: Phase 2 — re-exposure and reaction (symptomatic). On a later exposure, the allergen binds the IgE already sitting on mast cells, triggering histamine release.

Step 3: Map each environmental cause to where it feeds into the model …