Asthma Artwork of part of the respiratory system seen on an aerosol inhaler blue showing the effects of asthma The bronchi covered in bands of cartilage pink lead to smaller bronchiole airways that end in clusters of alveoli air sacs One of the clusters is seen in section revealing the sputum or phlegm yellow it contains In asthma a trigger such as an allergen causes the bronchioles to narrow and become inflamed This results in increased production of mucus further reducing the lungs oxygen capacity Asthma is treated by taking a bronchodilator drug to widen the bronchioles using an aerosol inhaler