Extrinsic Allergic Factor
Besides some of the factors causing allergy / asthma in a patient are: (i) house dust (present in bedrooms, mattresses, pillows, rugs, curtains, woollen clothes, blankets, carpets, upholstered furniture, etc.), (ii) moulds (which grow in humid places, like where there is a leakage of water in walls, roofs, filters of desert-coolers or airconditioners and places of poor ventilation like cowsheds, barns, etc.), (iii) pollens (from flowers, trees, grasses, weeds, etc.), (iv) dandruff from the skins of animals (i.e., scales from the outer parts of the skins of animals, like dogs, cats, cows, buffaloes, goats, sheeps, horses, etc.), (v) insect debris in the environment (house-flies, mosquitoes, cockroaches, ants, butterflies, etc.), (vi) feathers of birds (pigeons, feather pillows), (vii) various contact ants (like lipsticks, powders, soaps, perfumes, hair-dyes, shampoos, oils, creams, after-shave lotions, etc.), (viii) air pollutants (from ill-maintained engines of automobiles, like cars, two-wheelers, trucks, etc.)
Food allergy
Food allergy is also an important causative factor in many cases of asthma. Any food, like wheat, cereals, ice-cream, vegetables, non-vegetarian food, edible oils, fruits, milk, curd, ghee, eggs, coffee, cold drinks, etc. can cause allergy. Various condiments/spices used in the preparation of food may be the source of the allergy. Likewise, various preservatives used to preserve food articles may cause asthma. Coloring agents used in sweets, etc. too may prove harmful. Fermented food, like pickles, jams, beer, wines are other causes of food allergy. Even the metabolic by-products of ingested food may cause allergy. It is also seen that sometimes the patient is allergic to the outer covering of wheat, cereals, vegetables, etc. Hence a patient may be allergic to wheat, but not to maida, and similarly, one may be allergic to whole cereals, but not to the ones without outer shells.