Inhaled mold spores and particles from bird droppings and feathers (such as from parrots) can cause hypersensitivity (allergic) reactions in the bronchial tubes and the lungs. For example, when Aspergillus fungal spores cause an allergic reaction in the bronchial tubes, the condition is called allergic bronchopulmonary aspergillosis. Affected individuals have both asthma and bronchiectasis which require treatment with both bronchodilators and corticosteroids over a prolonged period of time. Sometimes antifungal therapy is used, as well. When the lung tissues develop an allergic reaction to inhaled bacteria, fungi, or bird particles, the condition is called hypersensitivity pneumonitis (HP). HP is differentiated from acute asthma by the lack of wheezing, the presence of a fever , and the pattern of pneumonia on the chest X-ray. HP is treated by avoiding the allergens and administering corticosteroids.
In 1952, . Peterson and . Murray of Upjohn developed a process that used Rhizopus mold to oxidize progesterone into a compound that was readily converted to cortisone.  The ability to cheaply synthesize large quantities of cortisone from the diosgenin in yams resulted in a rapid drop in price to US $6 per gram, falling to $ per gram by 1980. Percy Julian's research also aided progress in the field.  The exact nature of cortisone's anti-inflammatory action remained a mystery for years after, however, until the leukocyte adhesion cascade and the role of phospholipase A2 in the production of prostaglandins and leukotrienes was fully understood in the early 1980s.