Is Pulmonary Fibrosis Caused by Smoking?

Smoking does not single-handedly cause pulmonary fibrosis the way it causes lung cancer, but it is one of the strongest and most consistent risk factors for the disease. The relationship is more tangled than a simple cause-and-effect chain: some forms of pulmonary fibrosis are almost exclusively found in smokers, while the most common and feared form, idiopathic pulmonary fibrosis (IPF), develops through a mix of genetic susceptibility, environmental exposures, and cellular damage that smoking powerfully accelerates. Understanding where smoking fits in this picture matters for prevention, diagnosis, and what happens after a diagnosis is made.

How Smoking Relates to Idiopathic Pulmonary Fibrosis

IPF is the most common and most lethal type of pulmonary fibrosis, and cigarette smoking is one of its most recognized risk factors.1PubMed Central. Smoking and idiopathic pulmonary fibrosis A landmark case-control study found that people who had ever smoked were roughly 60 percent more likely to develop IPF than never-smokers, and the risk climbed with heavier use: those with a 21-to-40 pack-year history had more than double the odds.2PubMed. Cigarette smoking: a risk factor for idiopathic pulmonary fibrosis A large prospective study from the UK Biobank reinforced this, reporting that smokers had roughly twice the risk of developing pulmonary fibrosis compared with never-smokers.3Chest. Tobacco Smoking and Risk for Pulmonary Fibrosis: A Prospective Cohort Study From the UK Biobank

The word “idiopathic” means the cause is unknown, so by definition IPF cannot be pinned on any one trigger. Yet researchers have used a genetic technique called Mendelian randomization to test whether the link between smoking and IPF is likely causal rather than coincidental. That analysis found that a genetic predisposition to smoking was associated with a significantly higher risk of IPF, strengthening the case that smoking plays a direct biological role rather than merely tagging along with some other risk factor.4PubMed. Appraising the causal role of smoking in idiopathic pulmonary fibrosis: a Mendelian randomization study Still, many people with IPF have never smoked, and plenty of heavy smokers never develop the disease. Smoking loads the gun, but it does not always pull the trigger.

Lung Diseases That Smoking More Directly Causes

While the link between smoking and IPF is probabilistic, a separate group of interstitial lung diseases (ILDs) is so tightly bound to cigarette smoke that they almost never appear in nonsmokers. These conditions involve fibrosis, or lung scarring, and they are considered direct consequences of smoking rather than risk-factor associations.

The three main smoking-related ILDs are respiratory bronchiolitis-associated interstitial lung disease (RB-ILD), desquamative interstitial pneumonia (DIP), and pulmonary Langerhans cell histiocytosis (PLCH). Strong evidence supports a causal role for cigarette smoking in all three.5PubMed. Smoking-related interstitial lung disease: radiologic-clinical-pathologic correlation

The fibrosis in these conditions tends to be milder and more treatable than in IPF. On imaging, RB-ILD and DIP appear as diffuse ground-glass haziness rather than the dense honeycomb pattern that marks advanced IPF.12PubMed. Smoking-related interstitial lung diseases: radiologic-pathologic correlation There is also a distinct pattern called smoking-related interstitial fibrosis (SRIF) that pathologists sometimes find in lung tissue from smokers, which lacks the progressive architectural destruction seen in IPF.13Seminars in Diagnostic Pathology. Pathologic features of smoking-related lung diseases, with emphasis on smoking-related interstitial fibrosis and a consideration of differential diagnoses

What Cigarette Smoke Does to Lung Cells

Several overlapping biological pathways explain how smoking promotes scarring in lung tissue. These are not just theoretical: researchers have demonstrated them in human lung cells and animal models, and they help explain why the connection between smoking and fibrosis is consistent across so many different study designs.

Cigarette smoke damages the epithelial cells lining the air sacs. Experiments on human alveolar cells show that cigarette smoke extract disrupts the energy-producing machinery inside cells, triggers cell death through multiple pathways, and causes oxidative damage to cell membranes.14PLOS ONE. Human Alveolar Epithelial Cell Injury Induced by Cigarette Smoke This kind of damage is a precursor to fibrosis because the lung’s repair response can go haywire, laying down scar tissue instead of healthy cells.

Smoke also causes a type of internal cellular stress that pushes lung cells to behave abnormally. When a cell’s protein-folding machinery gets overwhelmed, it enters a state that can promote the transformation of normal lung cells into scar-producing cells called myofibroblasts. Laboratory studies have shown cigarette smoke extract does exactly this, ramping up the stress response and driving myofibroblast formation.15PubMed. Cigarette Smoke Extract Promotes Human Lung Myofibroblast Differentiation by the Induction of Endoplasmic Reticulum Stress This stress pathway is now considered a key contributor to IPF in general, whether or not smoking is involved, with environmental triggers like viruses and inhaled particles also capable of setting it off.16PubMed Central. Emerging evidence for endoplasmic reticulum stress in the pathogenesis of idiopathic pulmonary fibrosis

Another piece of the puzzle is premature aging of lung cells. Cigarette smoke accelerates the shortening of telomeres, the protective caps on the ends of chromosomes. A 2025 study found that smoke exposure in combination with lung injury led to significantly shortened telomeres and signs of cellular aging, compounding the fibrotic damage.17PubMed Central. Smoking Promotes AT2 Cell Senescence and Exacerbates Pulmonary Fibrosis by Downregulating POT1 via Integratively Inducing CpG Methylation and MECP2‑Mediated FOXP2 Transcriptional Binding Inhibition Separately, cigarette smoke has been shown to inactivate a longevity-related protein called SIRT1, driving the same aging-like changes in the cells that line the deepest part of the lungs.18Free Radical Biology and Medicine. Cigarette smoke-inactivated SIRT1 promotes autophagy-dependent senescence of alveolar epithelial type 2 cells to induce pulmonary fibrosis

Smoke also impairs the lung’s ability to clean up after cell death. Normally, healthy cells engulf and remove dead or dying neighbors through a process called efferocytosis. Cigarette smoke disrupts this cleanup by triggering internal stress that activates a protein called RhoA, which essentially freezes the cleanup machinery in place.19Scientific Reports. Cigarette smoke induces endoplasmic reticulum stress and suppresses efferocytosis through the activation of RhoA When dead cells accumulate instead of being cleared, they provoke ongoing inflammation and scar formation.

The Genetic Side of the Equation

Smoking alone cannot explain IPF, and genetics makes that clear. The most powerful genetic risk factor discovered so far is a variant near the MUC5B gene, which codes for a mucus protein. People carrying one copy of this variant had about 9 times the odds of developing IPF, and those with two copies had roughly 22 times the odds, compared with people without the variant.20PubMed Central. A common MUC5B promoter polymorphism and pulmonary fibrosis That dwarfs the roughly two-fold risk increase associated with smoking alone. The MUC5B variant is common enough that about 9 percent of the general population carries it, yet most of them never develop IPF, which underscores how fibrosis requires multiple hits.

Genetics and smoking do not operate in separate silos. Research on occupational exposures found a significant interaction between smoking and the MUC5B risk variant: people who carried the variant and smoked while working in exposed jobs had a particularly elevated risk, beyond what either factor would predict on its own.21PubMed. What role for asbestos in idiopathic pulmonary fibrosis? Findings from the IPF job exposures case–control study This kind of gene-environment interaction is why some smokers develop fibrosis while others do not.

When Fibrosis and Emphysema Develop Together

In some smokers, fibrosis and emphysema occupy different regions of the same lung, a pattern now recognized as combined pulmonary fibrosis and emphysema (CPFE). Patients with CPFE are predominantly men with a heavy smoking history who develop worsening shortness of breath on exertion and severely impaired gas exchange, even though their basic lung-volume tests may look surprisingly normal.22American Journal of Respiratory and Critical Care Medicine. Syndrome of Combined Pulmonary Fibrosis and Emphysema: An Official ATS/ERS/JRS/ALAT Research Statement The deceptively normal spirometry occurs because the stiffening effect of fibrosis and the hyperinflation of emphysema partially cancel each other out on standard tests, masking the severity of the underlying damage.

Clinically, these patients tend to develop a dramatic drop in blood oxygen during exercise and have a high rate of pulmonary hypertension, which worsens their prognosis. Fine crackles at the lung bases (from fibrosis) coexist with diminished breath sounds in the upper lungs (from emphysema), and clubbing of the fingers is common.23Mayo Clinic Proceedings. Combined Pulmonary Fibrosis and Emphysema: An Update CPFE is a powerful illustration of how smoking can drive two supposedly opposite forms of lung destruction simultaneously, and emerging evidence suggests the two diseases share overlapping genetic and molecular pathways.22American Journal of Respiratory and Critical Care Medicine. Syndrome of Combined Pulmonary Fibrosis and Emphysema: An Official ATS/ERS/JRS/ALAT Research Statement

Secondhand Smoke and Maternal Exposure

You do not have to smoke yourself to have your risk affected. Secondhand smoke introduces many of the same toxic compounds into the airways and is capable of inducing chronic inflammation and adverse immune changes that contribute to fibrotic lung disease.24Respiratory Medicine. Molecular mechanisms of passive smoking-induced respiratory diseases The UK Biobank study found that maternal smoking was also associated with a higher risk of pulmonary fibrosis in the offspring, with about a 38 percent increase in hazard for those whose mothers smoked.3Chest. Tobacco Smoking and Risk for Pulmonary Fibrosis: A Prospective Cohort Study From the UK Biobank This is a striking finding because it suggests that tobacco exposure during fetal development may prime the lungs for fibrotic disease decades later.

Occupational Dust and the Multiplier Effect

Smoking rarely acts alone. Workers exposed to inorganic dusts who are also heavy smokers face a risk of IPF far greater than either exposure would cause independently. A study of Swedish construction workers found that heavy smokers exposed to inorganic dust had roughly four times the risk of dying from IPF compared to light-smoking, unexposed workers.25PubMed. Smoking, occupational exposures, and idiopathic pulmonary fibrosis among Swedish construction workers A separate population-based study found that the combination of smoking, male sex, and occupational exposure raised the odds of severe pulmonary fibrosis to about 4.6 times those of unexposed nonsmoking women.26PubMed. Effects of smoking, gender and occupational exposure on the risk of severe pulmonary fibrosis: a population-based case-control study

These interactions matter for anyone who has both a smoking history and past exposure to asbestos, silica, metal dust, or wood dust. The lungs are dealing with multiple insults at once, and the damage compounds rather than simply adding up.

Does Quitting Smoking Help?

Quitting smoking does not reverse existing fibrosis, but it can slow the progression of interstitial lung diseases and reduce the risk of complications.27Tobacco Prevention and Cessation. Why making smoking cessation a priority for rare interstitial lung disease smokers? For smoking-related ILDs like RB-ILD and PLCH, stopping smoking is often the first and most important treatment step, and some patients see meaningful improvement from cessation alone. For IPF, the benefit is less dramatic because the disease has its own momentum once established, but continued smoking accelerates decline and worsens outcomes.

The challenge is that many people receive their fibrosis diagnosis years or decades after their peak smoking exposure. Former smokers carry elevated risk even after quitting, and the original case-control data showed the highest risk in former smokers rather than current ones.2PubMed. Cigarette smoking: a risk factor for idiopathic pulmonary fibrosis That may partly reflect a lag between exposure and disease, or it may reflect survival bias: the sickest current smokers may have already died of other causes. Either way, quitting is universally recommended, the earlier the better.

E-Cigarettes and Cannabis

Switching from cigarettes to e-cigarettes does not necessarily eliminate the fibrotic risk. Early clinical evidence has identified small-airway-centered fibrosis in e-cigarette users, including a pattern called constrictive bronchiolitis in which the small airways scar shut.28PubMed Central. E-Cigarette Use, Small Airway Fibrosis, and Constrictive Bronchiolitis Animal studies have found that subchronic vaping alters lung proteins in ways that overlap with biomarkers of both IPF and COPD.29American Journal of Respiratory Cell and Molecular Biology. Subchronic Electronic Cigarette Exposures Have Overlapping Protein Biomarkers with Chronic Obstructive Pulmonary Disease and Idiopathic Pulmonary Fibrosis Even the base liquid used in most e-cigarettes, vegetable glycerin, has been shown in mouse experiments to promote fibrotic changes and amplify lung inflammation on its own.30PubMed Central. The main e-cigarette component vegetable glycerin enhances neutrophil migration and fibrosis in endotoxin-induced lung injury via p38 MAPK activation This research is still in its early stages, and long-term human data on e-cigarettes and pulmonary fibrosis do not yet exist. But the early signals are not reassuring.

Cannabis smoke has received less attention, but a primate study comparing marijuana smoke, tobacco smoke, and placebo cigarettes found that all groups developed some epithelial changes, while the marijuana-exposed group showed a higher incidence and severity of bronchiolitis, abnormal cell growth, and fibrosis.31Elsevier (Archivos de Bronconeumología). Lung Disease Associated With Marijuana Use The amount of research here is thin compared to tobacco, but the mechanism is plausible: inhaling combustion products of any kind delivers particulate matter, oxidants, and irritants deep into the lungs.

Sex Differences in IPF and Smoking History

IPF is substantially more common in men. Data from the UK ILD registry show that about 78 percent of IPF patients are male, and men in the registry were more likely to have a smoking history than women with the same diagnosis (about 70 percent versus 60 percent).32PubMed. Gender differences in clinical features, comorbidities and prognostic outcomes in idiopathic pulmonary fibrosis—a retrospective cohort analysis from the British Thoracic Society Interstitial Lung Disease Registry The higher smoking rates in men likely explain some of that gap, but not all of it. Research into occupational co-exposures suggests the combined burden of smoking, dust exposure, and male sex creates an especially potent risk profile.26PubMed. Effects of smoking, gender and occupational exposure on the risk of severe pulmonary fibrosis: a population-based case-control study Women who develop IPF tend to be slightly younger at diagnosis and may have different clinical features, though the evidence on prognosis differences is still evolving.

When Smoking Interacts with Autoimmune Disease

Pulmonary fibrosis is not always idiopathic. It can develop as a complication of autoimmune diseases like rheumatoid arthritis, systemic sclerosis, and others. In rheumatoid arthritis, smoking appears to contribute to lung fibrosis through a dual mechanism: direct damage to the lining of the air sacs, promoting the release of scar-promoting signals, and stimulation of a chemical modification to proteins that drives the autoimmune response itself.33PubMed Central. Impact of cigarette smoking on rheumatoid arthritis-associated lung diseases: a retrospective case control study on clinical and radiological features and prognosis For someone with rheumatoid arthritis who also smokes, the lungs are being attacked from two directions at once: by the immune system and by the inhaled toxins.

This is worth knowing because people with autoimmune conditions often focus on their joint symptoms or skin manifestations without realizing their lungs are at risk too. Smoking cessation is even more urgent in this group, since it addresses both the direct lung injury and a driver of the underlying autoimmune process.

Written by

Tamara Boyd

At an outpatient pulmonary rehabilitation center in Rapid City, South Dakota, Tamara Boyd, RN, CCRN, leads breathing exercises for patients with fibrosis and COPD. Her work addresses living with COPD and long-term oxygen therapy. An 18-year pulmonary nurse, Boyd received her BSN from Sonoma State University.