Idiopathic pulmonary fibrosis (IPF) has no single confirmed cause, which is what “idiopathic” means. But decades of research have identified a clear pattern: in people with certain genetic vulnerabilities, repeated small injuries to the lungs trigger an abnormal healing response that replaces healthy tissue with stiff scar tissue. The condition is twice as common in men as in women, with a median age at diagnosis of 75. Each year, roughly 3 to 9 new cases per 100,000 people are diagnosed in Europe and North America.
How Lung Scarring Develops
Your lungs contain tiny air sacs called alveoli, lined with delicate cells that allow oxygen to pass into your bloodstream. In IPF, these lining cells suffer repeated microscopic injuries over time. Normally, damaged tissue heals and regenerates. In IPF, that repair process goes wrong.
Instead of rebuilding healthy tissue, the injured cells either die off or enter a state called senescence, where they stop dividing permanently but remain alive, pumping out chemical signals that attract inflammation and promote scarring. The lung gradually loses its ability to replace damaged cells with new ones. Scar tissue fills the spaces where air sacs used to be, making the lungs progressively stiffer and less able to transfer oxygen. This isn’t a one-time event. It’s a slow, ongoing cycle of injury and faulty repair that worsens over months and years.
Genetic Susceptibility
Genetics play a larger role in IPF than most people realize. The strongest known genetic risk factor is a variant in the promoter region of a gene called MUC5B, which is involved in producing mucus in the airways. People who carry one or two copies of this variant have 6 to 20 times the risk of developing IPF compared to those without it.
Telomere-related genes are the next most significant group. Telomeres are protective caps on the ends of chromosomes that shorten each time a cell divides. When they get too short, the cell can no longer replicate and either dies or becomes senescent. Variants in genes like TERT and TERC, which help maintain telomere length, are found in 20 to 30 percent of families with more than one member affected by pulmonary fibrosis. These variants cause telomeres to shorten prematurely, effectively aging lung cells faster than normal and exhausting the lung’s ability to regenerate after injury.
A smaller number of families (1 to 3 percent) carry variants in genes related to surfactant, the slippery coating that keeps air sacs from collapsing. At least 15 additional genetic variants have been identified that modestly increase IPF risk, including variants near genes involved in cell adhesion and immune signaling. No single gene “causes” IPF on its own, but the cumulative genetic burden helps explain why some people develop the disease and others with similar exposures do not.
Environmental and Occupational Exposures
Even with genetic susceptibility, something external typically needs to trigger the cycle of lung injury. Cigarette smoking is the most consistently identified environmental risk factor. Beyond smoking, occupational exposures to specific dusts and materials have been linked to higher IPF rates. These include wood dust (particularly pine), metal dust from brass, lead, and steel, and pesticides. The CDC has documented elevated IPF mortality in certain industries where these exposures are common.
Air pollution is an increasingly recognized contributor. Long-term exposure to fine particulate matter (PM2.5) and nitrogen dioxide appears to interact with genetic risk in a meaningful way. Research published in the European Respiratory Journal found that people with high genetic susceptibility who lived in heavily polluted areas had three times the risk of developing IPF compared to genetically low-risk individuals in cleaner environments. The study estimated that PM2.5 exposure alone could account for roughly 14 percent of IPF cases in the population studied. This gene-environment interaction helps explain why IPF clusters in certain regions and demographics.
Viral Infections
Chronic viral infections appear to be another trigger. A meta-analysis found that viral infection overall increased IPF risk by about 3.5 times. The viruses most strongly linked to IPF are members of the herpesvirus family: Epstein-Barr virus, cytomegalovirus, human herpesvirus 7, and human herpesvirus 8. These are common viruses that many people carry without symptoms, but in genetically susceptible individuals, persistent infection may cause ongoing low-level damage to the lung lining.
Importantly, it’s chronic or latent infections that seem to matter, not acute ones. The theory is that these viruses reactivate periodically in lung tissue, delivering the kind of repeated micro-injuries that drive the abnormal scarring process. Acute viral infections were not associated with IPF worsening once the disease was already established.
Acid Reflux and Micro-Aspiration
Gastroesophageal reflux disease (GERD) has a surprisingly strong connection to IPF. A genetic study using a method called Mendelian randomization found that GERD increases IPF risk by about 60 percent. The suspected mechanism is micro-aspiration, where tiny amounts of stomach acid and digestive enzymes repeatedly reach the lungs, particularly during sleep.
This isn’t just theoretical. When researchers analyzed fluid washed from the lungs of IPF patients, 62 percent had detectable levels of pepsin or bile acids, substances that should only be in the stomach. By comparison, only 25 percent of patients with other lung diseases had these markers, and none of the healthy comparison group did. The acid may damage the lung lining directly, and there’s evidence it could also disrupt mucus function tied to the MUC5B gene, impairing the lungs’ built-in defense system.
The Role of Aging
IPF is fundamentally a disease of aging lungs. The median diagnosis at age 75 is not a coincidence. Several of the biological processes that go wrong in IPF are the same ones that deteriorate with normal aging: telomeres shorten, cells accumulate damage they can’t repair, the machinery that clears out malfunctioning proteins becomes less efficient, and senescent cells build up in tissues.
In people with genetic variants that accelerate these processes, the lungs may reach a tipping point decades earlier than they otherwise would. Researchers have described the fibrosis as representing “an irreversible loss of tissue renewal capacity,” where the lung’s stem-like progenitor cells simply run out of the ability to divide and replace damaged tissue. At that point, the only response left is scarring. This framing of IPF as premature lung aging, amplified by genetic vulnerabilities and environmental insults, is now central to how researchers understand the disease.
Why “Idiopathic” Persists
With so many identified risk factors, it may seem odd that the disease retains “idiopathic” in its name. The label persists because no single cause is sufficient to explain IPF in any given patient. Two people can share the same MUC5B variant, the same smoking history, and the same occupational exposure, yet only one develops the disease. The current understanding is that IPF requires a convergence of factors: a genetic foundation that makes the lungs vulnerable, environmental or infectious triggers that deliver repeated injuries, and an aging biology that can no longer keep up with repair. In most individual cases, it remains impossible to point to one definitive cause, which is why the diagnosis is still one of exclusion, made after ruling out other known reasons for lung scarring.