What Is Fibrosis and How Does It Damage Organs?
Fibrosis is a slow buildup of tough, fiber-rich tissue inside an organ. It happens when the body keeps trying to repair damage that does not stop. Over time, this extra tissue crowds out working cells and leaves organs such as the liver, lungs, kidneys and heart stiff and less able to do their jobs.
By Chris Morais, MSc, MPhil, PhD
Published
Fibrosis develops when long-lasting injury keeps the body's repair system switched on. Cells called myofibroblasts lay down too much collagen and other support material, which takes the place of normal tissue. The organ becomes stiff, its blood supply can fall, and it slowly loses function. Early fibrosis can sometimes improve if the cause is removed.
- What Is Fibrosis?
- Is Fibrosis the Same as Scarring?
- What Causes Fibrosis?
- Which Cells Make Fibrous Tissue?
- What Builds Up in Fibrotic Tissue?
- How Does Fibrosis Stop Organs From Working Properly?
- Which Organs Can Be Affected by Fibrosis?
- Does Fibrosis Always Get Worse?
- Can Fibrosis Be Reversed?
- Frequently Asked Questions
What Is Fibrosis?
Fibrosis is the buildup of too much tough support material inside an organ, so that scar-like tissue takes the place of healthy tissue[1],[2]. This support material is called the extracellular matrix. It is the mesh of proteins that sits between cells and holds tissues together.
In a healthy organ, the matrix is kept in balance. Old matrix is broken down while new matrix is made. In fibrosis, that balance is lost. Far more matrix is made than is removed, and it builds up year after year.
Fibrosis is not a single disease. It is a process that can happen in almost any solid organ, including the liver, lungs, kidneys and heart[1]. It is the end point of many different long-term illnesses. Studies have estimated that diseases involving fibrosis caused about 18% of all deaths worldwide in 2019[2].
The overview article on what happens when cells and tissues are damaged shows where fibrosis fits among the body's responses to injury. This article looks more closely at how fibrosis develops, what it does to organs and whether it can be undone.
Is Fibrosis the Same as Scarring?
Fibrosis is a type of scarring, but it is not the same as the scar that forms after a cut. Making new matrix and then reshaping it is a normal part of healing[1]. The article on how the body heals a wound explains this process in the skin, from the first soft healing tissue to the final scar.
Fibrosis differs from a skin scar in three main ways:
- It happens inside organs. The extra tissue builds up within organs such as the liver, lungs, kidneys or heart. It is often spread through large areas of the organ, not limited to one spot.
- It keeps going. In normal healing, the cells that make scar tissue are cleared away once the job is done. In fibrosis, these cells stay and keep working[2].
- It replaces working tissue. A skin scar fills a gap left by an injury. Fibrosis slowly takes the place of the tissue that does the organ's work[2].
Put simply, a skin scar is repair that finishes. Fibrosis is repair that does not switch off.
What Causes Fibrosis?
Fibrosis is caused by injury that continues or keeps coming back over months or years[1]. A single, short injury that heals fully does not usually lead to it. The most common causes differ from organ to organ:
- Liver. Fatty liver disease linked to problems with metabolism, such as excess weight and type 2 diabetes; heavy alcohol use; and long-term infection with the hepatitis B or C virus[2],[3].
- Kidneys. Diabetes, high blood pressure and long-term inflammation of the kidney's tiny filters (glomerulonephritis)[2].
- Lungs. Environmental pollutants, certain medicines and some connective tissue diseases. In most people with lung fibrosis, no cause can be found[4].
- Heart. A heart attack, high blood pressure and diseases of the heart muscle. High blood pressure, diabetes and obesity together add to the risk[2].
Lung scarring caused by a medicine is uncommon. Doctors prescribe these medicines because their benefits outweigh this risk, and they watch for warning signs. Anyone worried about a medicine should talk to their doctor before stopping it.
How Does Long-Term Inflammation Lead to Fibrosis?
Long-term inflammation leads to fibrosis by sending a steady stream of repair signals that tell cells to make more matrix[1]. Inflammation is the body's first response to injury. Immune cells gather at the damaged area to clear dead cells and germs. When the injury goes on, this response never fully settles.
Macrophages, immune cells that swallow debris, play a large part. They can drive scarring at some stages of injury and help break scar tissue down at others[1]. When injury continues, the immune response often shifts toward a repair mode in which macrophages release signals that promote scarring[2].
One of the strongest of these signals is a growth factor called TGF-beta. It plays a leading role in turning ordinary support cells into myofibroblasts, the cells that make fibrous tissue[1]. As long as the injury and inflammation continue, more of these cells are switched on and more matrix is laid down.
Which Cells Make Fibrous Tissue?
Fibrous tissue is made mainly by myofibroblasts, which develop from cells already living in the organ[1],[2]. The main cells that can turn into myofibroblasts are:
- Fibroblasts. Support cells found in almost every organ. Normally, they make small amounts of matrix to keep tissue in good repair.
- Pericytes. Cells that wrap around the outside of tiny blood vessels[1],[2].
- Hepatic stellate cells. Storage cells found in the liver. In liver fibrosis, they are the main source of myofibroblasts[1],[2].
Some cells that travel from the bone marrow in the blood may also become fibrous-tissue-making cells, but how much they add is still unclear[2].
What Are Myofibroblasts?
Myofibroblasts are switched-on support cells that make large amounts of matrix and can also contract, pulling the tissue around them tighter[2]. They contain a muscle-type protein called alpha-smooth muscle actin, which gives them this pulling power[2].
In normal healing, myofibroblasts are only needed for a short time. Once repair is finished, most of them die in a planned, orderly way (a process called apoptosis), and immune cells clear them away[1]. In fibrosis, they do not leave. Ongoing injury signals keep them active, and they become better at resisting death[1],[2]. Every extra day they survive means more matrix and more pulling on the tissue.
What Builds Up in Fibrotic Tissue?
Fibrotic tissue fills up mainly with collagen, a tough, rope-like protein. Most of it is type I and type III collagen, along with fibronectin (a sticky protein that helps hold the mesh together) and proteoglycans (proteins with sugar chains attached that hold water)[2].
This thick, coarse matrix replaces the thin, delicate sheets (basement membranes) that normally sit beneath cells in healthy organs. These sheets are made of different materials, mainly type IV collagen and proteins called laminins[2].
Over time, enzymes link neighboring collagen fibers together. This is called cross-linking. Heavily cross-linked collagen forms a rigid structure that the body's own enzymes find much harder to break down[1]. This is one reason older fibrosis is harder to undo than new fibrosis.
How Does Fibrosis Stop Organs From Working Properly?
Fibrosis stops organs from working properly by replacing working tissue, making the organ stiff, reducing its blood supply and feeding its own growth. These effects build on one another:
- It replaces working cells. Fibrosis puts non-working scar tissue in place of working tissue[2]. In the liver, for example, scar tissue cannot make proteins, help fight infections or clean the blood the way healthy liver tissue does[3].
- It makes organs stiff. The extra matrix and the pulling of myofibroblasts stiffen the tissue[2]. In the lungs, the scarred tissue becomes thicker and stiffer. This makes breathing harder and can lower the amount of oxygen that reaches the blood[4]. In the heart, fibrosis can lead to heart failure and abnormal heart rhythms[2].
- It reduces blood flow. In the kidneys, fibrosis lowers function partly by reducing the blood supply[2]. In the liver, scarring can raise the pressure in the large vein that brings blood from the gut to the liver. This can cause enlarged veins in the food pipe and stomach that may suddenly bleed[3].
- It feeds itself. Stiff tissue pushes cells to make even more matrix, and low oxygen in scarred areas adds to the problem. This creates a loop that keeps the fibrosis going[2].
Which Organs Can Be Affected by Fibrosis?
Fibrosis can affect almost any solid organ[1]. The organs where it most often causes serious illness are the liver, lungs, kidneys and heart[2].
The table below compares fibrosis in these four organs.
| Organ | Common name | Common causes | Main effects |
|---|---|---|---|
| Liver | Cirrhosis (advanced scarring) | Fatty liver disease, heavy alcohol use, hepatitis B or C | Liver cannot make proteins or clean the blood well; high pressure in liver blood vessels |
| Lungs | Pulmonary fibrosis | Often no cause found; harmful dust, pollutants, some medicines | Shortness of breath, dry cough, less oxygen in the blood |
| Kidneys | Kidney (renal) fibrosis | Diabetes, high blood pressure, glomerulonephritis | Slow loss of filtering; can end in kidney failure |
| Heart | Cardiac fibrosis | Heart attack, high blood pressure, heart muscle disease | Stiff heart, heart failure, abnormal heart rhythms |
What Are Liver Cirrhosis, Lung Fibrosis and Kidney Fibrosis?
They are the names given to fibrosis in the liver, lungs and kidneys.
Liver cirrhosis is scarring of the liver[3]. It is the advanced stage of liver fibrosis. In the United States, the most common causes are long-term heavy drinking and hepatitis[3]. Possible problems include easy bruising or bleeding, swelling of the belly or legs, yellowing of the skin and eyes (jaundice) and kidney failure. If too much scar tissue forms, a liver transplant may be needed[3].
Lung fibrosis, also called pulmonary fibrosis, is scarring of the tissue deep inside the lungs, which becomes thicker and stiffer over time[4]. Common symptoms are shortness of breath, a dry cough that does not go away, tiredness, weight loss without trying and widening and rounding of the fingertips (clubbing)[4]. When no cause is found, it is called idiopathic pulmonary fibrosis[4]. This form mainly affects older adults[2].
Kidney fibrosis is the buildup of scar tissue inside the kidneys, which gradually replaces the tissue that filters the blood[2]. Many different kidney diseases, whatever their starting cause, end in kidney fibrosis. For this reason, it is often called the final common pathway to kidney failure[2].
Does Fibrosis Always Get Worse?
No, fibrosis does not always get worse, but it often does if its cause continues. The most important factor is whether the injury goes on.
When the injury continues, fibrosis tends to progress. In long-term kidney disease, for example, fibrosis is a progressive process that slowly reduces kidney function[2]. Lung fibrosis also tends to build up over time[4]. Once fibrosis is well established, the self-feeding loop of stiffness and low oxygen can help keep it going[2].
When the cause is removed or treated, fibrosis can slow down or stop. In cirrhosis, treating the cause can keep the scarring from getting worse[3]. How quickly fibrosis changes differs a great deal from person to person and from organ to organ. Finding it early gives the best chance of dealing with the cause before the scarring becomes advanced.
Can Fibrosis Be Reversed?
Fibrosis can sometimes be partly reversed, especially when it is found early and its cause is removed. Fibrosis was once thought to be permanent, but it is now known that it can fade in some cases[1].
The strongest evidence in people comes from the liver. When hepatitis B or C is treated, liver fibrosis has improved, even in some people who already had cirrhosis[1]. Improvement has also been seen in the kidneys and heart in some people once the underlying problem was treated[1].
When fibrosis fades, three things happen. Myofibroblasts either die or return to a resting state. Enzymes called matrix metalloproteinases cut up the extra collagen. Immune cells then clear away the debris[1].
There are limits. Old, heavily cross-linked collagen resists being broken down[1]. In established cirrhosis, the scar tissue usually does not disappear, although treating the cause can stop it from getting worse[3]. Pulmonary fibrosis currently has no cure, but treatments can ease symptoms and improve quality of life[4].
Treatment depends on the organ and the cause:
- Treating the cause. This is the most effective way to allow fibrosis to settle[1]. Examples include treating hepatitis, stopping heavy drinking and controlling blood sugar and blood pressure.
- Lung medicines. Two medicines, pirfenidone and nintedanib, are approved for idiopathic pulmonary fibrosis. They act on signals that drive scarring, but they have not been shown to make existing lung scars go away[1]. Oxygen therapy, lung exercise programs (pulmonary rehabilitation) and, for some people, a lung transplant are also used[4].
- Liver medicines. A medicine called semaglutide has been approved in the United States for adults with a form of fatty liver disease that has caused moderate to advanced liver fibrosis[2].
- Organ transplants. When an organ is badly scarred, a transplant may be the only option[3],[4].
Researchers are testing new medicines that aim to switch off myofibroblasts or help the body clear scar tissue, but these are still experimental[1],[2].
Frequently Asked Questions
Is fibrosis painful? Fibrosis itself often causes no pain, and many people have no symptoms in the early stages. Symptoms usually appear once the organ starts to struggle, and they depend on which organ is affected. Lung fibrosis, for example, causes shortness of breath and a dry cough[4], while advanced liver scarring can cause swelling of the belly and legs and easy bruising[3].
Is fibrosis a type of cancer? No, fibrosis is not cancer. It is a buildup of scar-like tissue, not the uncontrolled growth of abnormal cells. However, long-term scarring can raise the risk of some cancers. For example, a small number of people with cirrhosis develop liver cancer[3]. Many tumors also build dense, fibrous tissue around themselves as part of the tumor microenvironment.
Is cystic fibrosis the same as fibrosis? No, they are different conditions. Cystic fibrosis is an inherited disease of the mucus and sweat glands[5]. It mostly affects the lungs, pancreas, liver, intestines, sinuses and sex organs[5]. Its name comes from the scarring and fluid-filled sacs (cysts) it can cause in the pancreas, but its root cause is a gene change present from birth, not the injury-driven process described in this article.
How do doctors check for fibrosis? Doctors use different tests depending on the organ. For the liver, they use blood tests, imaging tests or a biopsy, in which a small piece of tissue is examined under a microscope[3]. Similar combinations of scans, organ function tests and, sometimes, biopsies are used for other organs.
Can stopping alcohol help liver fibrosis? Yes, stopping alcohol can help. Heavy alcohol use is one of the most common causes of liver scarring[3], and removing the cause of injury is the most effective way to let fibrosis settle[1]. Even when cirrhosis is already present, stopping can help keep it from getting worse[3]. People who drink heavily should get medical advice before stopping, because suddenly stopping can cause dangerous withdrawal symptoms.
Morais C. What Is Fibrosis and How Does It Damage Organs? [Internet]. BiologyWithin.com; 2026 Oct 20. Available from: https://www.biologywithin.com/2026/10/what-is-fibrosis-how-it-damages-organs.html
- Jun JI, Lau LF. Resolution of organ fibrosis. J Clin Invest. 2018;128(1):97-107.
- Pan Z, Zerehpoosh S, Wang SC, Örmeci N, Kim W, Eslam M. Beyond organ-specific therapies: a unified approach to multi-organ fibrosis. Drug Des Devel Ther. 2026;20:1-14.
- MedlinePlus. Cirrhosis. MedlinePlus, National Library of Medicine.
- MedlinePlus. Pulmonary Fibrosis. MedlinePlus, National Library of Medicine.
- MedlinePlus. Cystic Fibrosis. MedlinePlus, National Library of Medicine.
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Disclaimer: This article is for general educational purposes only and does not constitute medical advice, diagnosis, or treatment. Consult a qualified healthcare professional about personal health concerns.
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