Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disease in which scar tissue gradually replaces healthy lung tissue, making it increasingly difficult to breathe. The word “idiopathic” means the cause is unknown. It primarily affects adults over 50, carries a median survival of 2 to 5 years after diagnosis, and has no cure, though treatments can slow its progression.
What Happens Inside the Lungs
In healthy lungs, tiny air sacs called alveoli expand and contract with each breath, transferring oxygen into the bloodstream and releasing carbon dioxide. In IPF, the cells lining these air sacs become injured and trigger an abnormal healing response. Instead of repairing normally, the damaged cells transform into a type that behaves more like scar-producing tissue. This process, called epithelial-mesenchymal transition, is driven by a signaling protein that accelerates fibrosis.
Once this transformation begins, the new cells (called myofibroblasts) deposit large amounts of collagen and other structural proteins into the lung tissue. Over time, this buildup stiffens the lungs, thickens the walls of the air sacs, and reduces their ability to exchange oxygen. The scarring typically starts in the lower portions of both lungs and works inward, which is why early symptoms often feel mild before progressing steadily.
Who Gets IPF and Why
IPF is not rare. Pooled global incidence sits around 10.9 per 100,000 people, though rates vary widely by region. The United States has among the highest reported incidence at 27.6 per 100,000, while South Korea reports 2.4 per 100,000. Global prevalence is estimated at 37 per 100,000, with U.S. figures reaching roughly 58 to 61 per 100,000. The typical patient is male, over 60, and a current or former smoker.
Although the disease is labeled “idiopathic,” several risk factors increase the likelihood of developing it. The strongest known genetic risk factor is a variant in a gene called MUC5B. People carrying just one copy of this variant have roughly nine times the odds of developing IPF compared to those without it. Beyond genetics, environmental exposures play a role. Chronic inhalation of certain dusts, including metal, wood, and silica, has been linked to the disease. Smoking is a consistent risk factor, and occupational asbestos exposure can produce a nearly identical form of lung scarring.
Symptoms and Early Signs
The hallmark symptoms are a persistent dry cough and shortness of breath that worsens over months or years. Many people initially attribute the breathlessness to aging or being out of shape, which often delays diagnosis. The cough is typically nonproductive, meaning it doesn’t bring up mucus, and it can be one of the most frustrating day-to-day symptoms.
On physical examination, doctors listen for a distinctive sound called “Velcro crackles,” fine crackling noises heard through a stethoscope during inhalation. These are present in most IPF patients and sound similar to pulling apart a strip of Velcro. Another physical finding is digital clubbing, a widening and rounding of the fingertips and nails, which appears in 25 to 50% of patients. As the disease progresses, fatigue, unexplained weight loss, and aching joints or muscles may develop.
How IPF Is Diagnosed
Diagnosis relies heavily on a type of CT scan called high-resolution computed tomography (HRCT). Radiologists look for a specific scarring pattern known as usual interstitial pneumonia, or UIP. The classic features include honeycombing (clusters of small cystic air spaces with well-defined walls, often stacked in layers) and a reticular pattern of fine lines, both concentrated in the lower and outer portions of the lungs. When this pattern is clearly present on imaging and other known causes of lung scarring have been ruled out, a diagnosis can often be made without a lung biopsy.
If the CT findings are less definitive, showing a “probable” rather than definitive UIP pattern, a multidisciplinary team of pulmonologists, radiologists, and pathologists reviews the case together. Lung function tests measuring forced vital capacity (FVC), which reflects how much air you can forcefully exhale, establish a baseline and help track progression over time.
Conditions That Often Accompany IPF
IPF rarely exists in isolation. The scarring and inflammation affect other organ systems, and the medications and reduced activity levels compound the problem. Common cardiovascular comorbidities include coronary artery disease and pulmonary hypertension, which is elevated blood pressure in the arteries of the lungs. Gastroesophageal reflux disease (GERD) is strikingly common, though whether it contributes to the fibrosis or simply coexists is still debated.
About 30% of IPF patients also have emphysema, a combination that complicates lung function testing because emphysema causes overinflation while fibrosis causes stiffening. Patients with both conditions tend to have higher rates of pulmonary hypertension. People with IPF also face nearly five times the risk of developing lung cancer compared to the general population, with 3 to 22% of patients affected. Depression affects an estimated 12 to 49% of IPF patients, a range far higher than the 3.4% captured in insurance claims data, suggesting it is significantly underdiagnosed.
Treatment Options
Two medications are currently approved to slow the rate of lung function decline, though neither reverses existing scarring. Pirfenidone, taken as a daily oral dose, reduced the proportion of patients experiencing a significant drop in lung function (10% or more) or death by about 44% over one year in pooled clinical trial data. Patients on pirfenidone lost an average of 216 mL of lung capacity over a year, compared to 363 mL in those on placebo, a meaningful difference in the pace of decline.
Nintedanib, the other approved medication, works by blocking growth factor receptors involved in the scarring process. In pooled trial data, patients taking nintedanib twice daily experienced roughly half the annual rate of lung capacity decline compared to placebo (about 114 mL per year versus 224 mL). At one year, 47% of nintedanib-treated patients had a notable decline in lung function, compared to 61% on placebo. Both drugs cause side effects, most commonly gastrointestinal issues like nausea and diarrhea, and the choice between them often comes down to individual tolerability.
Supplemental oxygen becomes necessary as the disease advances and blood oxygen levels drop, particularly during exercise or sleep. Pulmonary rehabilitation, a structured program of exercise training, breathing techniques, and education, helps patients maintain physical function and quality of life even as lung capacity decreases.
Lung Transplantation
For patients with advanced disease, lung transplantation is the only option that can significantly extend survival. IPF is one of the most common reasons for lung transplant referral. Early referral matters because the evaluation process is lengthy, transplant waiting lists are long, and patients need to be healthy enough in other respects to survive the surgery.
Transplant centers evaluate candidates on several criteria. Other organs need to be functioning adequately. Most centers require a BMI between roughly 30 and 35 at the upper end. Candidates must be tobacco-free for at least six months and free of illicit substance use. A minimum level of physical endurance is expected, which is why staying active through pulmonary rehabilitation is important even when breathing is difficult. Centers also require patients to have two or three dedicated caregivers who can provide continuous support during recovery.
What Progression Looks Like
IPF follows a variable but generally downward trajectory. Some patients experience a slow, steady decline over several years. Others have periods of relative stability punctuated by acute exacerbations, sudden worsenings that can be life-threatening. The median survival of 2 to 5 years is a population-level statistic, and individual outcomes vary considerably based on age at diagnosis, baseline lung function, rate of decline, and response to treatment.
Lung function tests, particularly FVC, are the primary tool for tracking progression. A decline of 10% or more in FVC over six to twelve months is associated with a significantly worse prognosis. Doctors typically monitor FVC every three to six months to assess whether treatment is working and to time decisions about transplant referral or palliative care. Oxygen saturation during a six-minute walk test provides another practical measure of how the disease is affecting daily function.