If one is then exposed to colds, intense physical activity, air pollution, stimulating smells (like incense, perfume, or oil paints) or the humidity is too high or changes too suddenly, this can cause an increase in the glandular secretions in the air passage, leading to asthma.
如果再遇上感冒、劇烈運動，或是空氣濕度過高、氣溫突然升降（如三更半夜溫度驟降）等因素，也可能使氣管的分泌物增加，導致氣喘。