Asthma is believed to be caused by a complex interaction of genetic and environmental factors that can also influence its severity and responsiveness to medication. The condition is further classified into two general categories as extrinsic and intrinsic asthma depending on the stimuli of the attack.

(a) Extrinsic or Allergic Asthma: Asthma is extrinsic when it is triggered by an allergen. This is the most common type of asthma and is caused by pollutants, wood dust, smoke, chemicals, viral/bacterial infections, stress, emotion and even exercises that are capable of triggering the condition.

Most cases of Asthma in children are extrinsic caused by maternal smoking making the infants particularly vulnerable to allergic smoking. This condition is found more often in young boys than in girls.

(b) Intrinsic Asthma: Asthma is said to be intrinsic when it is not caused by any allergies/allergens. This condition is not likely to develop in children; its typical onset occurs after 40 years of age and is less responsive to medication when compared to allergic Asthma. The causes for this condition include respiratory irritants such as perfumes, cleaning agents, cold air, upper respiratory infections, and gastroesophageal reflux (GERD).

The above classification is further split into categories distinguishing one from another by means of severity and interactive response.

(i) Exercise induced Asthma (wheezing during physical activities.)
(ii) Nocturnal Asthma (respiring trouble while asleep, although the name relates to night.)
(iii) Occupational Asthma (work hazards, breathing chemical fumes and dust.)
(iv) Steroid resistant Asthma (unresponsiveness to medication as result of hyper-usage of steroids.)