People who suffer from asthma have difficulty breathing because the airways in their lungs contract when a trigger causes a reaction. Among the triggers of asthma are indoor and outdoor pollutants, according to doctors. Since pollution has become more common, the number of people affected by this disorder has risen. Indoor pollutants include cigarette smoke, dirt, insects, and even pets like dogs or cats. Outdoor pollutants include chemicals, dust, and smog, that is, smoke from factories or transport vehicles like buses and trucks.