Interstitial lung disease (ILD) is a group of more than 200 disorders that cause scarring or inflammation in the lungs, making it progressively harder to breathe. The damage targets the interstitium, the thin tissue that surrounds and supports the tiny air sacs where oxygen enters your bloodstream. As this tissue thickens or scars, less oxygen can pass through, and everyday activities like climbing stairs or walking across a parking lot become increasingly difficult.
How ILD Damages the Lungs
Your lungs contain millions of air sacs called alveoli. Each one is wrapped in a web of tiny blood vessels, separated by a paper-thin layer of tissue. In a healthy lung, oxygen passes effortlessly through this barrier into the blood. ILD disrupts that exchange.
The older understanding was that chronic inflammation drove the damage, but the current view is more nuanced. Something injures the delicate lining of the air sacs, whether it’s an infection, an inhaled toxin, radiation, or an autoimmune attack. The lung tries to heal, but the repair process goes wrong. Instead of restoring normal tissue, specialized cells called fibroblasts multiply and lay down excess collagen, creating stiff scar tissue. This is called fibrosis, and it makes the lungs rigid. Inflammation plays a role in many forms of ILD, but fibrosis can develop even without significant inflammation, which is one reason anti-inflammatory drugs alone don’t always work.
The scarring is generally irreversible. Once enough tissue has remodeled, gas exchange drops and oxygen levels fall. This is why early detection matters so much.
Types of Interstitial Lung Disease
ILD isn’t one disease. It’s an umbrella covering conditions that fall into a few broad categories.
Idiopathic (no known cause): The most recognized form is idiopathic pulmonary fibrosis (IPF), a chronic, progressive scarring disease with no identifiable trigger. Other idiopathic types include nonspecific interstitial pneumonia and cryptogenic organizing pneumonia. “Idiopathic” simply means doctors can’t pinpoint what started the process.
Autoimmune-related: Conditions like rheumatoid arthritis, systemic sclerosis (scleroderma), lupus, and Sjögren’s syndrome can cause the immune system to attack lung tissue. These forms are grouped as connective tissue disease-associated ILD. They can develop gradually or, in some cases, progress rapidly.
Exposure-related: Long-term inhalation of harmful substances is a well-established trigger. Asbestos dust from construction or mining, silica, mold, agricultural dust, and certain chemical fumes can all damage the interstitium over years of exposure. Some antibiotics, heart medications, and chemotherapy drugs can also trigger ILD, though this is uncommon.
Granulomatous: Sarcoidosis, a condition where clusters of inflammatory cells form in the lungs and other organs, is another form of ILD with its own distinct behavior and treatment path.
Symptoms and How They Progress
The most common symptom is breathlessness that comes on gradually. It often starts during physical activity and slowly worsens over months or years. A persistent dry cough is the other hallmark, and in some subtypes it’s the first thing people notice. Chest pain is uncommon overall but does occur in certain forms like sarcoidosis. Some people have no symptoms at all and are only flagged because a chest scan done for another reason looks abnormal.
Because the symptoms overlap with so many other conditions, from asthma to heart failure, ILD is frequently misdiagnosed or caught late. The gradual onset is part of the problem. Many people chalk up increasing breathlessness to aging or being out of shape before seeking evaluation.
Who Gets ILD
Globally, there were an estimated 390,000 new cases of ILD in 2021, with an incidence rate of about 4.55 per 100,000 people. That rate has been climbing steadily since 1990, rising roughly 20% for both men and women. High-income regions, including North America and parts of Asia and Latin America, report the highest rates, likely reflecting better diagnostic access and greater exposure to industrial pollutants.
Incidence rises sharply after age 45 and peaks between 50 and 75. Men tend to develop ILD at somewhat higher rates, particularly IPF, which disproportionately affects men over 60. Genetics also play a role. Certain gene variants related to the lung’s repair mechanisms and immune response increase susceptibility, especially in families with a history of pulmonary fibrosis.
How ILD Is Diagnosed
High-resolution CT scanning (HRCT) is the central diagnostic tool. It produces detailed cross-sectional images of the lungs and can reveal characteristic patterns of scarring, ground-glass opacities, or honeycombing that point toward a specific type of ILD. In many cases, the HRCT pattern is distinctive enough to make a diagnosis without further testing.
Pulmonary function tests measure how well your lungs move air and transfer oxygen, providing a baseline to track progression. Blood tests can identify autoimmune markers that suggest an underlying connective tissue disease. When imaging and lab work aren’t conclusive, a surgical lung biopsy may be needed. The gold standard for reaching a final diagnosis is a multidisciplinary team review, where pulmonologists, radiologists, and pathologists discuss the case together to reach a consensus.
Treatment Options
Treatment depends entirely on which type of ILD you have. For autoimmune-related ILD, medications that calm the immune system can slow or stop the lung damage. Tocilizumab, for example, was approved in 2021 specifically for ILD linked to scleroderma.
For fibrotic forms like IPF, antifibrotic medications are the primary treatment. These drugs slow the rate of scarring but don’t reverse damage that’s already happened. Two antifibrotics, nintedanib and pirfenidone, have been available for IPF for several years and are now also used for other forms of ILD where fibrosis is progressing. A newer option, nerandomilast, has been approved for IPF and progressive pulmonary fibrosis as well.
Supplemental oxygen becomes necessary when blood oxygen levels drop, especially during activity or sleep. For people with advanced disease who are otherwise good candidates, lung transplantation remains the only option that can restore normal breathing capacity.
Pulmonary Rehabilitation
Structured exercise programs designed for people with chronic lung disease offer significant benefits. Pulmonary rehabilitation typically combines aerobic exercise (walking, cycling, stepping), resistance training, breathing techniques, education about disease management, nutritional counseling, and psychological support.
The results are measurable. On average, people with ILD who complete a rehabilitation program can walk about 40 meters farther in a six-minute walk test, a meaningful improvement in daily function. Breathlessness decreases, exercise capacity improves, and quality-of-life scores improve substantially. These programs don’t reverse lung damage, but they help your body use the lung capacity you have more efficiently, and they give many people a greater sense of control over their condition.
Complications and Outlook
One of the most serious complications of ILD is pulmonary hypertension, or high blood pressure in the arteries of the lungs. As scarring restricts blood flow through the lungs, the right side of the heart has to pump harder. Over time, this can lead to right-sided heart failure. People who develop pulmonary hypertension alongside ILD tend to have more frequent flare-ups, reduced exercise tolerance, greater need for supplemental oxygen, and shorter survival.
Prognosis varies enormously depending on the type of ILD. Some forms, like certain drug-induced ILDs, can stabilize or improve once the trigger is removed. Others, like sarcoidosis, may resolve on their own. IPF sits at the other end of the spectrum. Without antifibrotic treatment, median survival from diagnosis is roughly 2 to 4 years. With early-stage disease, some patients survive nearly 7 years, while those diagnosed at an advanced stage may have a median survival closer to 2 years. Antifibrotics have improved these numbers, though IPF remains progressive and life-limiting.
For all forms of ILD, early diagnosis and ongoing monitoring make the biggest difference. The scarring process is much easier to slow down than to reverse, which is why persistent unexplained breathlessness or a dry cough that lingers for weeks deserves a thorough workup rather than a wait-and-see approach.