Interstitial lung disease is not a single illness, but rather an umbrella term for more than 200 different conditions that share one troubling feature: they cause inflammation and scarring in the delicate tissues of your lungs, making it progressively harder to breathe and get oxygen into your bloodstream.

What Is Interstitial Lung Disease?

Interstitial lung disease, often shortened to ILD, describes a large collection of lung disorders that damage the interstitium—the tissue surrounding the tiny air sacs in your lungs called alveoli. These air sacs are where oxygen moves from the air you breathe into your blood, and where carbon dioxide, a waste product, moves out. When the interstitium becomes inflamed and scarred, this critical exchange of gases becomes less efficient.^[1]

Your lungs are made of millions of these small air sacs working together. Around each air sac is a network of blood vessels and supportive tissue—the interstitium—that holds everything in place. In a healthy lung, this tissue is thin and flexible. When you have ILD, inflammation causes the interstitium to thicken and stiffen, almost like scar tissue forming after an injury. Over time, this scarring can become permanent and irreversible, making it harder for oxygen to pass through to your bloodstream.^[4]

ILD is also known as diffuse parenchymal lung disease, or DPLD. The term “diffuse” means the damage is spread throughout the lungs rather than concentrated in one spot. “Parenchymal” refers to the functional tissue of the lung—the parts that actually do the work of breathing.^[1]

Epidemiology

Interstitial lung disease affects a substantial number of people around the world, though exact numbers can be difficult to pin down because ILD encompasses so many different conditions. In 2015, ILD and a related condition called pulmonary sarcoidosis together affected approximately 1.9 million people globally. These diseases resulted in about 122,000 deaths that year.^[6]

In the United States, about 3 out of every 10,000 people are diagnosed with an ILD each year.^[4] Around 650,000 Americans currently live with some form of interstitial lung disease.^[16] These numbers likely underestimate the true burden, as some people may have mild disease that goes undiagnosed, or their symptoms may be mistaken for other conditions.

ILD can affect anyone, but certain demographic patterns emerge. The disease is more common in people over the age of 70, and men are more likely to develop ILD than women. This may be partly because men historically have had higher rates of smoking and occupational exposures to lung-damaging substances.^[1]

The most common type of ILD is called idiopathic pulmonary fibrosis, or IPF, which means lung scarring with no identifiable cause. After IPF, the next most common forms are those caused by workplace exposures to harmful substances or those linked to autoimmune and connective tissue diseases like rheumatoid arthritis or scleroderma.^[1]

Causes

The causes of interstitial lung disease are typically divided into two broad categories: known causes and unknown causes. When doctors can identify what triggered the lung damage, it’s called a known cause. When they cannot find any clear reason, the condition is labeled as idiopathic, which simply means “of unknown origin.”^[1]

Among the known causes, environmental and occupational exposures stand out as major contributors. Long-term breathing in of certain substances can have a toxic effect on the lungs. Mineral dusts such as asbestos, silica (found in sand and rock), coal dust, and beryllium are well-documented causes of ILD. People who work in mining, construction, sandblasting, or manufacturing may be at particular risk. Organic dusts, including mold spores and particles from bird droppings, can also trigger lung inflammation and scarring over time. Even toxic gases like methane or cyanide can damage airways and lung tissue through direct injury or by generating harmful molecules in the body.^[5]

Connective tissue diseases and other autoimmune conditions represent another important cause of ILD. Diseases like rheumatoid arthritis, lupus, and scleroderma can cause the body’s immune system to attack its own tissues, including the lungs. This autoimmune attack can affect all parts of the lung—the airways, the air sacs, and the supporting tissue—leading to inflammation and scarring.^[1][5]

Certain medications can also cause lung damage. More than 350 drugs have been linked to pulmonary complications, including some chemotherapy drugs, certain antibiotics, and other medications. Radiation therapy, particularly when used to treat cancers in the chest area, can lead to radiation pneumonitis, a type of lung inflammation that may progress to scarring.^[1][5]

Other known causes include granulomatous diseases like sarcoidosis, where clusters of inflammatory cells form in the lungs and other organs. Allergic reactions to substances in the environment can cause a condition called hypersensitivity pneumonitis. Even some infections can lead to ILD, though this is less common.^[1]

Despite extensive testing, doctors cannot always identify what caused a person’s ILD. In these cases, particularly when the scarring follows certain patterns, the diagnosis may be idiopathic pulmonary fibrosis. This is the most common form of ILD, yet its root cause remains a mystery. Researchers believe genetic factors, environmental exposures, and abnormal healing responses may all play a role.^[1]

Risk Factors

Several factors can increase your chances of developing interstitial lung disease. Age is one of the most significant risk factors—people over 70 are far more likely to be diagnosed with ILD than younger individuals. This may be because the cumulative effects of exposure to irritants and the natural aging process make older lungs more vulnerable to damage.^[1]

Being male also increases your risk. Men develop ILD more often than women, possibly due to higher historical rates of smoking and greater likelihood of working in occupations with exposure to lung-damaging substances.^[1]

Smoking is a major risk factor for many forms of lung disease, including ILD. Both current smokers and people who smoked in the past face elevated risk. Smoking not only directly damages lung tissue but can also worsen existing ILD and lead to serious complications like lung cancer.^[1]

Certain medical conditions increase susceptibility to ILD. People with a history of hepatitis C, tuberculosis, pneumonia, chronic obstructive pulmonary disease (COPD), or connective tissue diseases like rheumatoid arthritis or scleroderma have higher risk. These conditions may trigger immune system changes or chronic inflammation that makes the lungs more prone to scarring.^[1]

Occupational and environmental exposures represent another critical risk factor. Working in jobs where you breathe in asbestos, silica dust, molds, fungi, bacteria, or other irritants over long periods substantially increases your chances of developing ILD. Industries like mining, construction, agriculture, and manufacturing are particularly high-risk.^[1]

Having received chest radiation, such as radiation therapy for cancer treatment, can damage lung tissue and lead to scarring months or even years after the treatment ends. The risk depends on the dose of radiation, the area treated, and individual susceptibility.^[1]

Symptoms

The symptoms of interstitial lung disease usually develop gradually. In the early stages, you might not notice anything at all, or symptoms may be so mild that you dismiss them. However, as the disease progresses, symptoms typically become more noticeable and bothersome. Understanding these symptoms is important because by the time some types of ILD cause obvious symptoms, lasting lung damage may have already occurred.^[2]

The most common symptom is shortness of breath, medically called dyspnea. At first, you might only feel breathless during physical activity or exercise—climbing stairs, walking uphill, or doing housework might leave you winded. As the disease worsens, breathlessness can occur with less and less exertion, and eventually even while resting. This happens because the scarred, stiffened lung tissue cannot expand properly and cannot efficiently transfer oxygen to your blood.^[1][2]

A persistent dry cough is another hallmark symptom of ILD. Unlike a cough from a cold or infection that produces mucus, the cough in ILD is typically dry and hacking. It can be annoying and distressing, often worsening at night or during physical activity. This cough occurs because the damaged lung tissue and inflammation irritate the airways.^[1][2]

Fatigue is very common among people with ILD. You may feel tired all the time, even after a full night’s sleep. This overwhelming tiredness happens because your body isn’t getting enough oxygen to fuel your cells and organs. Without adequate oxygen, even simple daily tasks can feel exhausting.^[1]

Chest discomfort or tightness may also occur. Some people describe a feeling of pressure or heaviness in the chest. This sensation is distinct from the sharp pain associated with a heart attack, but it can still be uncomfortable and worrying.^[1]

Additional symptoms may appear depending on the underlying cause of your ILD. Some people experience unintentional weight loss or poor appetite. Others may notice clubbing—a rounding or widening of the fingertips and toes that occurs when tissues don’t receive enough oxygen over a long period.^[11]

Symptoms tend to be mild at first but worsen over months or years. The speed at which symptoms progress varies widely depending on the specific type of ILD. Some forms remain stable or worsen very slowly, while others, like idiopathic pulmonary fibrosis, can progress rapidly and unpredictably.^[1]

Prevention

While not all forms of interstitial lung disease can be prevented—especially those with unknown causes—there are several steps you can take to reduce your risk or slow the progression of disease if you’ve already been diagnosed.

If you smoke, quitting is the single most important action you can take. Smoking directly damages lung tissue and can worsen any existing ILD, increasing your risk of complications like lung infections and lung cancer. Stopping smoking can help slow disease progression and improve your quality of life. Many resources are available to help you quit, including counseling programs, medications, and support groups.^[10][12]

Avoiding secondhand smoke is also important. If you live with someone who smokes, encourage them to smoke outside or to quit. Spending time in smoke-filled environments can irritate your lungs and contribute to further damage.

If your work exposes you to dust, chemicals, fumes, or other lung irritants, take protective measures seriously. Use appropriate respiratory protection equipment such as masks or respirators. Ensure your workplace follows safety regulations for ventilation and dust control. If you’ve been diagnosed with ILD due to occupational exposure, you may need to change jobs or modify your work environment to avoid further harm.^[1][13]

At home, be mindful of potential irritants. Keep your living space well-ventilated and free from mold. If you have hobbies that expose you to dust or fumes—such as woodworking, painting, or working with chemicals—use proper ventilation and protective gear. Avoid exposure to bird droppings if you have birds as pets or encounter them in your environment, as these can trigger certain types of ILD.^[13]

Getting vaccinated is an important preventive measure for people with or at risk for ILD. Respiratory infections can cause serious complications in people with compromised lung function. Annual flu vaccines, pneumococcal vaccines to prevent bacterial pneumonia, and COVID-19 vaccines can all help protect you from infections that could lead to more lung damage, hospitalizations, or even life-threatening complications.^[13]

If you have an autoimmune or connective tissue disease that puts you at risk for ILD, work closely with your healthcare providers to manage that condition effectively. Proper treatment of the underlying disease may help prevent or slow lung involvement.

Regular medical check-ups and monitoring are essential, especially if you have risk factors for ILD. Early detection allows for earlier treatment, which may help slow disease progression and prevent complications. If you develop new symptoms like persistent cough or unexplained shortness of breath, seek medical attention promptly rather than dismissing them as normal aging.^[2]

Pathophysiology

Understanding what happens inside the lungs during interstitial lung disease helps explain why symptoms develop and why treatment is so important. The pathophysiology—the changes in normal body function caused by disease—of ILD involves a complex process of inflammation and scarring that fundamentally alters how your lungs work.

In healthy lungs, when you breathe in, air travels down your windpipe and through branching airways into millions of tiny air sacs called alveoli. These alveoli are surrounded by an intricate network of tiny blood vessels called capillaries. Between the alveoli and the capillaries lies the interstitium—a thin layer of tissue containing connective tissue, blood vessels, and immune cells. This interstitium normally acts like a delicate mesh, providing structural support while allowing oxygen and carbon dioxide to pass through easily.^[4]

When ILD develops, this orderly process breaks down. The disease usually begins with inflammation in the interstitium. This inflammation can be triggered by various factors—inhaled irritants, autoimmune reactions, drug effects, or unknown causes. Immune cells flood into the tissue, releasing chemicals that cause swelling and damage.^[2][5]

In a normal healing response, inflammation is temporary and the tissue repairs itself. But in ILD, the healing process becomes abnormal and excessive. Instead of restoring the tissue to its original thin, flexible state, the body produces too much scar tissue, a process called fibrosis. This scar tissue is thick and stiff, like the scar that forms on skin after a deep cut, but it happens inside the delicate structures of your lungs.^[2]

As fibrosis progresses, the interstitium thickens dramatically. The thin membrane that once allowed easy gas exchange becomes a thick barrier. The alveoli themselves may become distorted or destroyed. In advanced disease, the normal lung architecture is replaced by thick bands of scar tissue and cyst-like spaces, a pattern called honeycombing that can be seen on imaging tests.^[6]

This scarring has direct consequences for breathing and oxygen delivery. The thickened interstitium makes it harder for oxygen molecules to travel from the air in the alveoli to the blood in the capillaries. At the same time, carbon dioxide cannot escape from the blood as efficiently. The stiffened, scarred lungs cannot expand as much during breathing, reducing the amount of fresh air that enters with each breath.^[4]

As oxygen levels in the blood drop, your body tries to compensate. Your heart may have to work harder to pump blood through the lungs, which can lead to increased pressure in the blood vessels of the lungs—a condition called pulmonary hypertension. Over time, this increased pressure strains the right side of the heart, potentially leading to right-sided heart failure.^[13]

The reduced oxygen supply affects your entire body. Without enough oxygen, your muscles tire easily, your brain may feel foggy, and every physical task becomes more difficult. This explains why fatigue and shortness of breath are such prominent symptoms of ILD.

The scarring process in most forms of ILD is irreversible. Once fibrosis has replaced normal lung tissue, that tissue cannot be restored to its original state. This is why early detection and treatment are so critical—the goal is to slow or stop new scarring before more lung function is lost.^[1][2]