MASH stands for metabolic dysfunction-associated steatohepatitis, a progressive form of liver disease in which fat buildup triggers inflammation and damage to liver cells. It affects roughly 5 to 14% of the general population and is closely tied to conditions like obesity and type 2 diabetes. If the name sounds unfamiliar, you may recognize its former name: NASH, or nonalcoholic steatohepatitis. Global liver experts officially replaced that term in 2023.
Why the Name Changed From NASH
For decades, this condition fell under the umbrella of “nonalcoholic fatty liver disease,” or NAFLD. That label had several problems. It defined the disease by what it wasn’t (not caused by alcohol) rather than what it was. It also excluded patients who drank any meaningful amount of alcohol, even though many of those people had the same metabolic drivers and faced equal or greater risk. Those patients were left out of clinical trials and research efforts despite being at higher risk for liver-related complications and death.
The language itself was also a barrier. In a large international survey of liver specialists and patients, 61% of respondents found “nonalcoholic” potentially stigmatizing, and 66% said the same about “fatty.” Using the word “fatty” to describe a medical condition discouraged some patients from seeking care or discussing their diagnosis. The new framework, MASLD (metabolic dysfunction-associated steatotic liver disease) as the broad category and MASH as its inflammatory subtype, names the actual cause of the disease: metabolic dysfunction. It also acknowledges that alcohol-related liver disease and metabolic liver disease share overlapping biology and can coexist in the same person.
What Happens Inside the Liver
MASH begins when excess fat accumulates in liver cells. On its own, some fat in the liver (known as simple steatosis) is relatively common and often harmless. MASH is different because that fat triggers a damaging chain reaction. Under sustained metabolic stress, liver cells become injured and start to swell, a hallmark change pathologists call “hepatocyte ballooning.” Those injured cells release reactive oxygen species and distress signals that recruit immune cells to the area, creating chronic inflammation.
Over time, this cycle of injury and inflammation produces scar tissue, or fibrosis. The scarring replaces healthy liver tissue and, if it continues unchecked, can progress to cirrhosis, where the liver becomes so scarred it can no longer function properly. MASH is now the second leading cause of liver transplantation and end-stage liver disease.
Who Gets MASH
About 38% of all adults worldwide currently have MASLD, the broader category of metabolic liver disease. By 2040, that number is projected to exceed 55%. MASH, the more severe inflammatory form, is far more common in people with type 2 diabetes. While 5 to 14% of the general population has MASH, that figure jumps to roughly 37% among people with type 2 diabetes, and some recent analyses put it even higher, around 66% in diabetic populations.
The link between MASH and type 2 diabetes runs in both directions. Insulin resistance drives fat accumulation in the liver, and a fatty, inflamed liver worsens insulin resistance throughout the body. Obesity, high blood pressure, and elevated blood lipids all increase risk. The condition is also increasingly recognized in children and adolescents, with 7 to 14% of young people now estimated to have some form of metabolic liver disease.
Symptoms Are Often Absent
Most people with MASH have no symptoms at all during the early stages. When symptoms do appear, they tend to be vague: persistent fatigue, a general feeling of being unwell, or mild discomfort in the upper right side of the abdomen. These are easy to attribute to other causes, which is why the disease frequently goes undiagnosed for years.
Symptoms become more noticeable once significant scarring or cirrhosis develops. At that point, people may experience itchy skin, swelling in the abdomen or legs, shortness of breath, yellowing of the skin and eyes, and visible spider-like blood vessels beneath the skin. In advanced cases, the buildup of toxins the liver can no longer filter causes confusion, slurred speech, and excessive sleepiness. By this stage, the damage is difficult to reverse.
How MASH Is Diagnosed
Because symptoms are unreliable, diagnosis typically starts with blood tests and imaging. Simple blood-based scoring tools combine routine lab values (like platelet count and liver enzyme levels) with age to estimate fibrosis risk. These screening tools work best for ruling out advanced scarring rather than confirming it. A specialized blood panel called the ELF score measures proteins related to scar formation and offers somewhat better accuracy, though it still has limitations.
Liver biopsy remains the definitive way to diagnose MASH. Under a microscope, pathologists look for the three hallmarks: fat accumulation, inflammation, and ballooned liver cells, along with the degree of fibrosis. Non-invasive alternatives like elastography, which uses ultrasound or MRI to measure liver stiffness, are increasingly used as a middle step between blood tests and biopsy.
Cardiovascular Risk Matters Most
One of the most important and often surprising facts about MASH is that liver failure is not the most common cause of death for people with the condition. Roughly 40% of deaths among MASLD patients are attributed to cardiovascular events like heart attacks and strokes. Only 4 to 8% are caused by liver cancer or cirrhosis. This means that managing heart health, including blood pressure, cholesterol, and blood sugar, is just as critical as addressing the liver itself.
Treatment Options
Weight loss is the most effective lifestyle intervention. Losing at least 10% of body weight, whether through diet, exercise, or bariatric surgery, is associated with resolution of MASH and regression of liver scarring. That’s a meaningful amount of weight loss, and maintaining it long-term is the real challenge for most people. Even more modest losses of 5 to 7% can reduce liver fat, though they’re less likely to reverse inflammation and fibrosis.
In March 2024, the FDA approved the first medication specifically for MASH. Sold under the brand name Rezdiffra (resmetirom), it works by activating a thyroid hormone receptor concentrated in the liver. This receptor plays a central role in how the liver processes fat. Stimulating it reduces the amount of fat stored in liver cells. The drug is approved for adults with moderate to advanced scarring (stages F2 to F3) who do not yet have cirrhosis, and it’s meant to be used alongside diet and exercise, not as a replacement for them.
Beyond medication, managing the metabolic conditions that drive MASH is essential. Controlling blood sugar, treating high blood pressure, and lowering cholesterol all slow disease progression and reduce the cardiovascular risk that accounts for the majority of deaths in this population. For people who already have cirrhosis, treatment focuses on preventing complications and, in severe cases, evaluating eligibility for liver transplantation.
Living With MASH
Because MASH progresses slowly over years or decades, regular monitoring matters more than any single test result. If you’ve been diagnosed, expect periodic blood work, imaging, or elastography to track whether fibrosis is stable, improving, or advancing. The pace of progression varies widely between individuals, and not everyone with MASH will develop cirrhosis.
The practical takeaway is that MASH is both a liver disease and a metabolic disease. Treating it effectively means addressing the whole metabolic picture: body weight, physical activity, blood sugar, and heart health. The liver damage is real and can become irreversible, but for most people, the window for meaningful intervention is wide.