Smoking directly causes several forms of interstitial lung disease. At least four distinct ILD subtypes are classified as smoking-related, and in some of them, more than 90% of patients are current or former smokers. Beyond these specific diseases, smoking also increases the risk of developing other forms of ILD that can occur in nonsmokers too.
Types of ILD Caused by Smoking
Interstitial lung disease isn’t a single condition. It’s an umbrella term for a group of disorders that cause inflammation and scarring in the tissue surrounding the air sacs in your lungs. Several of these are tied so closely to smoking that they rarely occur in nonsmokers.
The major smoking-related ILDs include:
- Pulmonary Langerhans cell histiocytosis (PLCH): Accounts for 3% to 5% of all ILD cases. More than 90% of people diagnosed with PLCH are cigarette smokers. This condition triggers the overgrowth of specific immune cells that damage lung tissue.
- Respiratory bronchiolitis-associated ILD (RB-ILD): Makes up 2% to 3% of ILD cases. This involves inflammation centered around the small airways.
- Desquamative interstitial pneumonia (DIP): A rare form representing less than 1% of all ILD. Despite “pneumonia” in the name, it’s a chronic scarring condition, not an infection.
- Combined pulmonary fibrosis and emphysema (CPFE): A syndrome where the upper portions of the lungs develop emphysema while the lower portions develop fibrosis. It accounts for 5% to 10% of ILD cases and predominantly affects men aged 65 to 70 with heavy smoking histories.
How Smoking Damages the Lung’s Scaffold
The tissue between and around your lung’s air sacs (the “interstitium”) is a thin, delicate scaffold that supports gas exchange. Cigarette smoke damages this scaffold through a chain reaction at the cellular level. Smoke triggers the energy-producing structures inside lung cells to release harmful molecules called reactive oxygen species, essentially flooding cells with oxidative stress. This disrupts how cells process and break down fats, causing fat to accumulate inside the cells and activating a type of cell called a fibroblast.
Fibroblasts are the cells responsible for producing scar tissue. Once activated, they begin laying down collagen, the same structural protein found in scars on your skin, but in the delicate tissue of your lungs where flexibility is essential for breathing. Over time, this scarring stiffens the lungs and makes it harder to absorb oxygen.
In DIP, pathologists can literally see the damage under a microscope. The air sacs fill with immune cells called macrophages that contain a distinctive brown pigment referred to as “smoker’s pigment.” These “smoker’s macrophages” pack the air spaces uniformly throughout the lungs, and the walls between air sacs thicken with inflammation. In marijuana smokers who develop DIP, the pigment looks slightly different: smaller, golden-brown particles.
How Much Smoking Is Enough to Cause ILD?
Heavy, long-term smoking carries the greatest risk. Among people diagnosed with CPFE, over 90% report a smoking history of more than 40 pack-years (roughly a pack a day for 40 years, or two packs a day for 20 years). Most fall in the 40 to 60 pack-year range. However, lighter smoking histories can still lead to other smoking-related ILDs like RB-ILD and DIP, which tend to appear in younger, less heavy smokers.
Genetics also play a role. A common variant in a gene called MUC5B nearly triples the odds of developing interstitial lung abnormalities in current or former smokers (odds ratio of 3.2). Even nonsmokers carrying this variant have more than double the odds (2.4 times). So while smoking and genetics each independently raise your risk, carrying the variant and smoking creates a particularly unfavorable combination.
Secondhand Smoke as a Risk Factor
There is early evidence linking passive smoke exposure to ILD, particularly exposure during childhood. In one study of ILD patients, those who had been exposed to secondhand smoke in infancy were diagnosed at younger ages, around 50 compared to nearly 55 for those without early exposure. This suggests that breathing in tobacco smoke during critical periods of lung development may set the stage for disease decades later, though the research in this area is still limited compared to direct smoking studies.
What Smoking-Related ILD Feels Like
The symptoms tend to come on gradually, which is one reason these conditions often go undiagnosed for months or years. Progressive shortness of breath during activity is the hallmark. You might also develop a dry cough that doesn’t respond to typical treatments. In PLCH specifically, some people experience a collapsed lung (pneumothorax) as the first sign of the disease.
On imaging, the patterns vary by type. CT scans of someone with RB-ILD may show ground-glass opacities (hazy patches), subtle scarring patterns, or in some cases look nearly normal. CPFE has a distinctive split appearance: destroyed, air-filled lung tissue in the upper lobes and dense scarring in the lower lobes. These patterns help doctors distinguish smoking-related ILD from other causes of lung scarring.
Quitting Smoking as Treatment
For RB-ILD, stopping smoking is often the only treatment needed. Many patients see improvement on both imaging and lung function tests after quitting, without any medication. This makes RB-ILD one of the more reversible forms of interstitial lung disease, provided the damage hasn’t progressed too far.
DIP also requires smoking cessation as a first step, but it typically needs additional treatment with anti-inflammatory medication for cases that don’t improve with quitting alone. The disease sits on a spectrum: some cases can partially reverse, while others progress to more permanent scarring despite treatment.
CPFE and advanced fibrosis are a different story. Once significant scarring has developed in the lower lungs, that damage is largely irreversible. Treatment at that stage focuses on slowing further progression and managing symptoms like low oxygen levels. PLCH can stabilize or even partially regress after quitting, but some patients develop progressive lung destruction regardless.
The common thread across all these conditions is that continuing to smoke accelerates the damage. Quitting doesn’t guarantee reversal, but it’s the single most important intervention for every form of smoking-related ILD.