Pulmonary fibrosis is a chronic lung disease in which scar tissue builds up in the lungs, making them stiff and increasingly difficult to breathe with over time. About 18 out of every 100,000 people worldwide have the most common form, idiopathic pulmonary fibrosis (IPF), with rates nearly double that in North America. The scarring is permanent, but treatments can slow its progression and help people maintain their quality of life longer.
How Lung Scarring Develops
Healthy lungs contain tiny air sacs called alveoli, where oxygen passes into your bloodstream and carbon dioxide passes out. In pulmonary fibrosis, repeated injury to the cells lining these air sacs triggers an abnormal repair process. Instead of healing normally, the damaged tissue activates cells called fibroblasts, which transform into a more aggressive version called myofibroblasts. These cells behave like wound-repair cells that never shut off, continuously depositing collagen, the same structural protein found in scars on your skin.
Over time, this excess collagen accumulates and thickens the walls of the air sacs. The delicate, flexible tissue that once allowed easy gas exchange becomes rigid and thick. The air sacs collapse, the lung architecture is destroyed, and less and less oxygen can reach the bloodstream. This is why shortness of breath worsens progressively: the lungs physically cannot do their job anymore.
Known Causes and Risk Factors
In many cases, doctors cannot identify a specific cause. When no trigger is found, the condition is called idiopathic pulmonary fibrosis, and it accounts for the largest share of diagnoses. IPF typically affects people over 50 and is more common in men and in people with a history of smoking.
When a cause can be identified, it generally falls into a few categories:
- Occupational exposures: Regularly inhaling inorganic dusts like asbestos, silica, coal dust, beryllium, or hard metal dusts can damage lung tissue over years. This form is called pneumoconiosis.
- Environmental triggers: Breathing in mold spores, bacteria, or animal proteins (particularly from indoor or caged birds) can cause a form called hypersensitivity pneumonitis, where the lungs react with inflammation that eventually leads to scarring.
- Autoimmune diseases: Rheumatoid arthritis and systemic sclerosis (scleroderma) are the two autoimmune conditions most frequently linked to lung fibrosis. Lupus, Sjögren’s disease, and dermatomyositis can also cause it, though less commonly.
- Medications and radiation: Certain chemotherapy drugs and radiation therapy to the chest can damage lung tissue enough to trigger fibrosis.
Symptoms: Early and Late
The earliest and most common symptom is shortness of breath during physical activity. At first, it might only show up during exercise or climbing stairs, and many people attribute it to aging or being out of shape. A persistent dry cough that doesn’t produce mucus is the other hallmark early symptom. Because these signs are vague, the average person lives with symptoms for one to two years before receiving a diagnosis.
As the disease progresses, breathing difficulty worsens and begins affecting everyday tasks like getting dressed or walking short distances. Fatigue becomes significant. Some people develop clubbing, a widening and rounding of the fingertips and nail beds caused by chronic low oxygen levels. When a doctor listens to the lungs with a stethoscope, they often hear a distinctive crackling sound during inhalation, commonly described as “Velcro-like” because it resembles the sound of pulling apart Velcro strips. This finding, combined with progressive breathlessness, is one of the strongest clinical clues.
How It Is Diagnosed
Diagnosis centers on a type of CT scan called high-resolution CT (HRCT), which produces detailed cross-sectional images of the lungs. Doctors look for specific patterns in how the scarring is distributed and what it looks like. The most characteristic pattern, called usual interstitial pneumonia or UIP, shows scarring concentrated in the lower and outer portions of the lungs with a distinctive “honeycombing” appearance, clusters of small, air-filled cysts that look like a honeycomb on the scan. When this pattern is clearly present, doctors can be more than 90% confident in the diagnosis without needing a lung biopsy.
If the scan shows scarring with thickened airways but no honeycombing, the pattern is classified as “probable UIP,” which still carries 70% to 89% confidence. Less clear patterns may require additional testing, including blood work to rule out autoimmune diseases or, in some cases, a surgical lung biopsy. Pulmonary function tests, which measure how much air you can inhale and how efficiently oxygen transfers into your blood, help establish baseline lung function and track progression over time.
Prognosis and Disease Course
The outlook for pulmonary fibrosis depends heavily on the type and how early it’s caught. For IPF specifically, the prognosis without treatment is serious: median survival is two to three years, and five-year survival in Western countries has historically ranged from 20% to 40%. These numbers, however, reflect an era before effective medications were available.
With current antifibrotic treatments, the picture has improved. A Japanese study following 91 patients found a median survival of 53 months (about four and a half years) from the first hospital visit. Among patients who stayed on treatment for at least a year, the five-year survival rate reached 52%, and the two-year survival rate was 89%. The disease does not progress at the same rate in everyone. Some people remain relatively stable for years, while others experience a faster decline. Acute flare-ups, called exacerbations, can cause sudden worsening and are a major driver of poor outcomes.
Medications That Slow Progression
Two antifibrotic medications are approved specifically for pulmonary fibrosis, and both work by interfering with the scarring process rather than reversing existing damage.
The first blocks the signaling molecule that tells fibroblasts to transform into scar-producing cells. By dampening this signal, it slows the rate at which new collagen is deposited in the lungs. The second works differently, targeting multiple growth factor receptors on fibroblasts to prevent them from multiplying. A meta-analysis found that this second medication reduced the rate of lung function decline by roughly 51%.
Neither drug is a cure. Their primary benefit is slowing the pace of decline, preserving the lung function you still have for as long as possible. Side effects are common, particularly gastrointestinal issues like nausea and diarrhea, which lead some people to need dose adjustments. Starting treatment early, before significant lung function is lost, gives these medications the most room to work.
Pulmonary Rehabilitation
Structured exercise programs designed for people with lung disease, known as pulmonary rehabilitation, consistently improve daily functioning even though they don’t change the underlying scarring. Multiple randomized trials have shown that patients who complete rehabilitation programs can walk significantly farther on a standard six-minute walking test. One study found patients gained an average of 46 meters (about 150 feet) of additional walking distance after a 10-week program, and another showed this improvement held steady at a six-month follow-up.
Beyond walking distance, rehabilitation reduces the sensation of breathlessness during activity and improves quality-of-life scores. The connection between the two is strong: in one study, improvements in walking capacity correlated tightly with improvements in how patients rated their overall well-being. The benefits are most pronounced immediately after completing a program and tend to fade over time if exercise isn’t maintained, which is why ongoing physical activity matters.
Lung Transplantation
For people whose lung function continues to decline despite medication, lung transplantation is the only option that can substantially extend life. Current guidelines recommend referral to a transplant center when forced vital capacity drops below 80% of predicted values or when the lungs’ ability to transfer oxygen into the blood falls below 40% of normal. Other triggers for referral include needing supplemental oxygen during exercise or at rest, worsening symptoms despite treatment, or a confirmed diagnosis of the most aggressive scarring patterns.
Transplant evaluation is a lengthy process involving extensive testing of heart, kidney, and liver function alongside psychological assessment and nutritional status. Because donor lungs are scarce and the wait can be long, early referral is critical. Pulmonary fibrosis is now one of the leading reasons for lung transplantation worldwide, and outcomes have improved as surgical techniques and post-transplant care have advanced.