Certain factors affect your risk of developing hypersensitivity pneumonitis. These factors include age, environment or occupation, family history and genetics, lifestyle habits, other medical conditions, and sex or gender.
Although hypersensitivity pneumonitis can occur at any age, people tend to be diagnosed with this condition between 50 and 55 years of age. Hypersensitivity pneumonitis is a common type of chronic interstitial lung disease in children.
Repeated exposure to certain substances that cause the condition, possibly while working in occupations where environmental sources are common, can increase your risk of developing hypersensitivity pneumonitis. Certain occupations—such as farmers or people who breed animals or birds, cheese washers, woodworkers, and wine makers—have a greater chance of exposure to causative substances. However, you may be exposed to environmental sources in your home or elsewhere. Even having pets such as birds in the home can increase your risk of hypersensitivity pneumonitis.
Alone, environmental exposure to causative substances is not enough to cause hypersensitivity pneumonitis. An estimated 85 to 95 percent of people exposed to causative substances either never develop hypersensitivity pneumonitis or they experience a mild immune reaction with no obvious signs or symptoms or disease.
Genetics is thought to predispose some people to have strong immune responses and develop hypersensitivity pneumonitis after repeat exposures to a causative substance. In some populations, family history of pulmonary fibrosis or hypersensitivity pneumonitis may increase the risk of developing hypersensitivity pneumonitis. When hypersensitivity pneumonitis occurs in relatives it is called familial hypersensitivity pneumonitis.
Researchers are beginning to map genetic variations in immune system proteins that may increase the risk for developing hypersensitivity pneumonitis. These differences may explain why immune cells respond differently between people who do or do not develop hypersensitivity pneumonitis after the same exposure to a causative substance.
Smoking is not thought to increase the risk of developing hypersensitivity pneumonitis. However, smoking can worsen chronic hypersensitivity pneumonitis and cause complications. If you have hypersensitivity pneumonitis, learn why doctors recommend quitting smoking.
Some viral infections later in life may increase the risk of developing hypersensitivity pneumonitis.
Men and women can have hypersensitivity pneumonitis. Some small studies found this condition to be slightly more common in women.