Steatohepatitis is a form of liver disease where fat buildup in the liver triggers inflammation and cell damage. Unlike simple fatty liver, which is relatively harmless on its own, steatohepatitis means the liver is actively being injured. Left unmanaged, it can progress to scarring (fibrosis), cirrhosis, and liver failure. About 30% of the global population has some degree of fatty liver disease, and steatohepatitis represents the more dangerous end of that spectrum.
How Steatohepatitis Develops
A healthy liver contains small amounts of fat. Problems begin when fat accumulates in more than 5% of liver cells, a condition called hepatic steatosis or simply “fatty liver.” For many people, the story stops there. But in others, the excess fat sets off a chain reaction of damage.
The leading explanation is sometimes called the “two-hit” model. The first hit is the fat itself accumulating in liver cells. The second hit is oxidative stress, a process where unstable molecules damage cell membranes and trigger inflammation. Fat-laden liver cells become vulnerable to this kind of injury, and when it happens, they swell up in a characteristic way pathologists call “ballooning.” These swollen, dying cells release chemical signals that attract waves of immune cells, including white blood cells called macrophages, neutrophils, and T cells, into the liver tissue. The immune response, meant to clean up the damage, ends up causing even more harm and can stimulate scar-forming cells in the liver to lay down fibrous tissue.
This cycle of fat accumulation, cell injury, immune activation, and scarring is what distinguishes steatohepatitis from simple fatty liver. It is an active, progressive process rather than a static condition.
Metabolic vs. Alcohol-Related Forms
Steatohepatitis comes in two main forms depending on the cause. Metabolic dysfunction-associated steatohepatitis (MASH, formerly called NASH) is driven by metabolic conditions like obesity, insulin resistance, type 2 diabetes, high blood pressure, and abnormal cholesterol levels. Alcohol-associated steatohepatitis (ASH) results from heavy drinking, generally defined as 20 grams or more of alcohol daily for women and 30 grams or more for men (roughly two to three standard drinks).
Under a microscope, the two forms look remarkably similar, with fat, inflammation, and ballooned liver cells present in both. ASH tends to show a few distinctive features, including certain patterns of bile duct damage and thicker bands of scar tissue. But the overlap is significant enough that telling them apart often relies more on a patient’s drinking history than on the biopsy itself. Some people have both metabolic risk factors and significant alcohol use, making diagnosis especially tricky. The distinction matters because treatment strategies differ: one centers on metabolic health, the other on stopping alcohol use.
The 2023 renaming from NASH to MASH was part of a broader effort to describe fatty liver disease by what causes it rather than by what it isn’t. The old term “nonalcoholic” defined the condition only by the absence of alcohol, which many experts felt was stigmatizing and imprecise. The newer terminology focuses on the metabolic dysfunction at the root of the disease.
Who Is at Risk
The metabolic form of steatohepatitis is closely tied to conditions that cluster together under the umbrella of metabolic syndrome. The most common risk factors are obesity, type 2 diabetes, insulin resistance, high blood pressure, and dyslipidemia (abnormal levels of cholesterol or triglycerides). In a large Medicare analysis of over 10 million patients, 85.5% of those with fatty liver disease had hypertension, 84.1% had dyslipidemia, and 55.5% had diabetes.
Men are more frequently affected than women. Globally, fatty liver disease prevalence runs about 36.6% in men compared to 25.5% in women. The condition is not limited to any single region: prevalence is roughly 30% across Asia, Europe, and North America, with South America potentially higher at around 34%.
Insulin resistance deserves special mention because it appears to be the metabolic engine behind much of the disease. When cells stop responding normally to insulin, the body compensates by producing more of it. This excess insulin promotes fat storage in the liver and activates inflammatory pathways that push simple steatosis toward steatohepatitis.
How It Progresses Over Time
Not everyone with steatohepatitis will develop serious liver damage, but the risk is real and substantial. In the Medicare study, the cumulative risk of progressing from fatty liver disease to cirrhosis was 39% over eight years. Among those who reached early-stage cirrhosis, 45% went on to develop decompensated cirrhosis, where the liver can no longer perform its basic functions. The mortality figures paint an even starker picture: 12.6% for fatty liver disease overall, 31.1% for cirrhosis, and 76.2% for liver cancer.
The independent predictors of progression included cardiovascular disease, kidney impairment, dyslipidemia, and diabetes. This reinforces that steatohepatitis is not purely a liver problem. It is a systemic metabolic disease, and the conditions that accompany it accelerate its course. Heart disease, not liver failure, is actually the leading cause of death in people with fatty liver disease.
How Steatohepatitis Is Diagnosed
Liver biopsy remains the most definitive way to diagnose steatohepatitis. A pathologist examines a tiny sample of liver tissue under a microscope and looks for three hallmarks: fat accumulation, inflammation (clusters of immune cells in the liver tissue), and ballooned hepatocytes. They also assess the degree of fibrosis. A scoring system combines major factors (ballooning and fibrosis, each weighted double) with minor factors (lobular inflammation, microgranulomas, and a specific nuclear change in liver cells) to produce a numerical score. Scores of 6 or above indicate steatohepatitis, while scores of 4 to 5 fall in a borderline zone.
Because biopsy is invasive and carries a small risk of complications, there has been a major push toward non-invasive alternatives. The most widely used is a specialized ultrasound device that measures liver stiffness (a proxy for scarring) and fat content in a single exam. When combined with a blood marker of liver inflammation called AST, it produces what’s known as a FAST score, which can identify people with significant fibrotic steatohepatitis without a needle. Other scoring systems incorporate insulin resistance measurements, specific proteins released by damaged liver cells, or even MRI-based assessments of liver fat and stiffness. One blood-based panel achieved diagnostic accuracy as high as 93.2% in its original study, though that dropped to about 79% when tested in other patient groups.
These non-invasive tools are especially useful for screening and monitoring over time, but a biopsy is still often needed to confirm the diagnosis and guide treatment decisions in borderline or complex cases.
Weight Loss and Lifestyle Changes
Weight loss is the single most effective intervention for metabolic steatohepatitis. The key threshold is 10% of total body weight. In a study of patients with biopsy-confirmed steatohepatitis, 63.2% of those who lost at least 10% of their body weight saw their liver fibrosis improve, compared to just 9.1% of those who lost less. That is a dramatic difference, and it underscores that modest weight loss (5% to 7%) may reduce liver fat but often isn’t enough to reverse the inflammation and scarring that define steatohepatitis.
Reaching and maintaining 10% weight loss is difficult for most people, which is part of why steatohepatitis has been so challenging to treat. A combination of dietary changes, regular physical activity, and in some cases weight-loss medications or bariatric surgery may be needed. No single diet has been proven superior, but reducing processed foods, added sugars, and saturated fats while increasing fiber and whole foods consistently shows benefits in clinical studies.
The First Approved Medication
For decades, there was no FDA-approved drug specifically for steatohepatitis. That changed in March 2024 with the approval of resmetirom (brand name Rezdiffra), a once-daily pill indicated for adults with non-cirrhotic steatohepatitis and moderate to advanced fibrosis. The drug works by activating a specific thyroid hormone receptor in the liver, which helps the organ burn off excess fat and reduce inflammation.
In clinical trials, 26% to 36% of patients taking resmetirom achieved resolution of their steatohepatitis without worsening fibrosis at 12 months, compared to 9% to 13% on placebo. Fibrosis improvement without worsening inflammation occurred in 23% to 28% of treated patients versus 13% to 15% on placebo. These are meaningful improvements, though they also show that the drug doesn’t work for everyone. It is prescribed alongside diet and exercise, not as a replacement for lifestyle changes. Dosing is weight-based: 80 mg daily for people under 100 kg and 100 mg daily for those at or above that weight.
The approval of resmetirom marks a turning point for steatohepatitis treatment, and several other drugs targeting different mechanisms are in late-stage clinical trials. For the first time, people with this condition have a pharmacological option backed by rigorous evidence.