Examples include autoimmune disorders, viral infections and bacterial infection like tuberculosis which may cause fibrotic changes in both lungs upper or lower  lobes and other microscopic injuries to the lung. However, pulmonary fibrosis can also appear without any known cause. In this case,  it is termed "idiopathic". Most idiopathic cases are diagnosed as idiopathic pulmonary fibrosis. This is a diagnosis of exclusion of a characteristic set of histologic/pathologic features known as usual interstitial pneumonia (UIP). In either case, there is a growing body of evidence which points to a genetic predisposition in a subset of patients. For example, a mutation in surfactant protein C (SP-C) has been found to exist in some families with a history of pulmonary fibrosis. Autosomal dominant mutations in the TERC or TERT genes, which encode telomerase, have been identified in about 15 percent of pulmonary fibrosis patients.Diseases and conditions that may cause pulmonary fibrosis as a secondary effect include:
Inhalation of environmental and occupational pollutants, such as metals in asbestosis, silicosis and exposure to certain gases. Coal miners, ship workers and sand blasters among others are at higher risk. Hypersensitivity pneumonitis, most often resulting from inhaling dust contaminated with bacterial, fungal, or animal products
Cigarette smoking can increase the risk or make the illness worse
Some typical connective tissue diseases such as rheumatoid arthritis, ankylosing spondylitis, SLE and scleroderma
Other diseases that involve connective tissue, such as sarcoidosis and granulomatosis with polyangiitis
Infections, including COVID-19
Certain medications, e.g.
Hyposmia, or microsmia, is a reduced ability to smell and to detect odors. A related condition is anosmia, in which no odors can be detected. Some of the causes of olfaction problems are allergies, nasal polyps, viral infections and head trauma. In 2012 an estimated 9.8 million people aged 40 and older in the United States had hyposmia and an additional 3.4 million had anosmia/severe hyposmia.Hyposmia might be a very early sign of Parkinsons disease. Hyposmia is also an early and almost universal finding in Alzheimers disease and dementia with Lewy bodies. Lifelong hyposmia could be caused by Kallmann syndrome or Autism Spectrum Disorder. Along with other chemosensory disturbances, hyposmia can be a key indicator of COVID-19. Epidemiology
The National Health and Nutrition Examination Survey (NHANES) collected data on chemosensory function (taste and smell) in a nationally-representative sample of US civilian, non-institutionalized persons in 2012. Olfactory function was assessed on persons aged 40 years and older with an 8-item, odor identification test (Pocket Smell Tests™, Sensonics, Inc., Haddon Heights, NJ). Odors included food odors (strawberry, chocolate, onion, grape), warning odors (natural gas, smoke) and household odors (leather, soap). Olfactory function score was based on the number of correct identifications. Prevalence (%) of anosmia/severe hyposmia (scores 0 to 3) was 0.3 at age 40-49 rising to 14.1 at age 80+. Prevalence of hyposmia (scores 4 to 5) was much higher: 3.7% at age 40-49 and 25.9% at 80+. Both were more prevalent in individuals of African descent than in those of Caucasian descent.