A new study has provided some of the clearest evidence yet of how smoking physically damages human lungs.
For the first time, scientists directly measured how smoking changes the mechanical behavior of real human lung tissue and found that smoking makes the lungs significantly stiffer, similar to the damage seen in fibrosis, a serious lung disease that causes scarring.
The research was led by scientists at University of California, Riverside and published in the Journal of the Royal Society Interface.
Lungs are made up largely of soft, spongy tissue called lung parenchyma. This tissue expands and contracts every time a person breathes. Healthy lung tissue needs to stay flexible so oxygen can move easily into the bloodstream while carbon dioxide is removed from the body.
When lungs become stiff, breathing becomes harder because the tissue resists expansion. This can reduce oxygen delivery throughout the body and make simple activities feel exhausting.
Smoking has long been linked to diseases such as chronic obstructive pulmonary disease, emphysema, lung cancer, and fibrosis. However, scientists previously had limited information about exactly how smoking changes the physical behavior of human lung tissue itself.
To investigate this question, researchers used lungs donated either for transplantation or scientific research. They carefully removed small square samples of lung parenchyma and stretched the tissue in different directions while measuring how strongly it resisted movement.
The researchers discovered major differences between smokers and nonsmokers.
Lung tissue from smokers became much stiffer when stretched, resisting expansion more strongly than healthy tissue from nonsmokers. According to the researchers, this behavior closely resembles fibrosis, where scar tissue builds up and gradually makes breathing more difficult.
Study leader Mona Eskandari, a mechanical engineer at UC Riverside, explained that previous studies often relied on animal models or stretched tissue in only one direction. But real lungs expand in many directions at the same time during breathing.
To better copy natural breathing, Eskandari’s laboratory stretched the tissue across multiple directions simultaneously. This allowed the team to study lung mechanics in a way that more closely reflects how human lungs actually behave inside the body.
The study also revealed another surprising discovery: different parts of the lungs behave differently.
Researchers found that tissue from the upper areas of the lungs was generally stiffer than tissue from lower regions, even within the same lung lobe.
The scientists believe gravity may help explain this difference. Because humans spend most of their lives upright, the upper and lower lungs experience different long-term physical forces over time.
This uneven stiffness may help explain why some lung injuries affect certain regions more severely than others. For example, patients using ventilators sometimes develop ventilator-induced lung injury when parts of the lungs become overstretched. The findings suggest that some lung regions may naturally be more vulnerable to mechanical stress.
The researchers also studied how lung tissue responds during repeated stretching cycles.
They found that human lung tissue loses more energy during repeated movement than lung tissue from mice. This may explain why animal experiments do not always accurately reflect how human lungs behave.
This discovery is especially important because scientists are increasingly building advanced computer models called “digital twin” lungs. These models are designed to simulate breathing, disease progression, and medical treatments.
Eskandari explained that if these computer models rely only on animal data, they may fail to fully capture the true mechanics of human lungs.
The research team also observed early signs that lungs may become stiffer with age, although they emphasized that more research is needed to confirm this finding.
One challenge for the study was the limited number of donor lungs available for this type of detailed testing. Human lungs suitable for research are rare, making it difficult to study very large numbers of samples.
Even so, the researchers say this study provides one of the most detailed collections of mechanical data ever gathered from human lung tissue.
The findings may eventually help improve ventilator design, lung surgery planning, and computer models used to predict how diseased lungs respond to stress and treatment.
Eskandari founded the biomechanics Experimental and Computational Health laboratory, also called the bMECH laboratory, at UC Riverside to study how biological tissues behave mechanically.
Overall, the study offers important new evidence about the physical damage smoking causes inside human lungs. One major strength of the research is that it directly examined human lung tissue instead of relying mainly on animal models.
However, because donor lungs are difficult to obtain, larger studies will still be needed to better understand how smoking, aging, and disease affect lung stiffness over time.
If you care about lung health, please read studies about marijuana’s effects on lung health, and why some non-smokers get lung disease and some heavy smokers do not.
For more information about health, please see recent studies that olive oil may help you live longer, and vitamin D could help lower the risk of autoimmune diseases.
Source: University of California, Riverside.
