MASH has two widely known meanings. In its original and most familiar use, MASH stands for Mobile Army Surgical Hospital, the frontline medical units made famous by the long-running TV series. In modern medicine, MASH stands for Metabolic dysfunction-Associated Steatohepatitis, a serious form of liver disease. Which meaning applies depends entirely on context, but both are worth understanding.
MASH as a Military Term
The U.S. Army Medical Department developed the Mobile Army Surgical Hospital as its frontline surgical facility following World War II. A MASH unit was a 60-bed mobile hospital, fully staffed with surgical and medical personnel and equipped to perform life-saving surgery and postoperative care for soldiers too badly injured to be moved. These units operated closest to combat zones, where speed and proximity made the difference between life and death.
MASH units became a permanent part of American culture through the 1970 Robert Altman film and the CBS television series M*A*S*H, which ran from 1972 to 1983 and remains one of the most-watched shows in TV history. The series was set during the Korean War, and its final episode drew over 105 million viewers. For most people searching “what does MASH stand for,” this is the answer they’re looking for.
MASH as a Medical Term
In 2023, major liver disease organizations worldwide officially renamed a condition previously known as NASH (nonalcoholic steatohepatitis) to MASH: Metabolic dysfunction-Associated Steatohepatitis. The name change was led by a coalition that included the American Association for the Study of Liver Diseases, the European Association for the Study of the Liver, and several patient advocacy groups.
MASH is a liver disease that develops when fat buildup in the liver triggers inflammation and cell damage. It goes beyond simple fatty liver. To qualify as MASH, a liver biopsy needs to show three things: fat accumulation in liver cells, swollen and damaged liver cells (called “ballooning”), and clusters of inflammatory cells scattered through the liver tissue.
Why the Name Changed From NASH to MASH
The old name, “nonalcoholic fatty liver disease,” had two problems. First, it defined the condition by what it wasn’t (not caused by alcohol) rather than what it was. Second, both patients and healthcare providers considered the word “fatty” stigmatizing. The renaming initiative, which ran from 2020 through 2023, involved hepatology societies across the Americas, Europe, and Asia-Pacific, along with patient organizations and regulatory bodies.
The new name is affirmative: it points directly to the metabolic problems driving the disease. The vast majority of cases previously labeled NAFLD are linked to metabolic factors like insulin resistance, obesity, and abnormal cholesterol levels. “Metabolic dysfunction-associated” captures that connection without stigmatizing language.
Who Is at Risk for MASH
The metabolic criteria that define MASH risk are specific. You meet the threshold if you have type 2 diabetes, or if you have obesity (a BMI of 30 or higher, or 25 or higher for people of Asian descent) along with at least one additional metabolic risk factor. Those risk factors include fasting blood sugar at or above 100 mg/dL, blood pressure at or above 130/85, elevated triglycerides (150 mg/dL or higher), or low HDL cholesterol (below 40 for men, below 50 for women). Waist circumference also plays a role, with cutoffs of 102 cm for men and 88 cm for women (lower in Asian populations).
How MASH Progresses
MASH is graded by fibrosis, which is the amount of scarring in the liver. This staging system is the single most important factor in determining long-term outcomes. The stages run from F0 (no scarring) through F1 (mild), F2 (moderate), and F3 (advanced scarring) to F4, which is cirrhosis. At F4, the liver is so heavily scarred that it can no longer function properly, and the risk of liver failure and liver cancer rises sharply.
Many people with early-stage MASH have no symptoms at all. The disease is often discovered incidentally through blood tests or imaging done for other reasons. By the time symptoms like fatigue, abdominal discomfort, or unexplained weight loss appear, significant liver damage may already be present.
Treatment Options
For most of its history, MASH had no approved medication. Treatment centered on lifestyle changes: weight loss of 7 to 10 percent of body weight can reduce liver fat and inflammation, and sustained weight loss can even reverse fibrosis in some cases.
That changed in 2024 when the FDA approved the first medication specifically for MASH with moderate to advanced fibrosis. The drug, sold under the brand name Rezdiffra, works by activating a thyroid hormone receptor concentrated in the liver, which helps reduce the triglyceride buildup driving the disease. It’s taken as a daily pill, with the dose based on body weight. It’s not a replacement for lifestyle changes but an additional tool for people whose liver scarring has already progressed to a concerning stage.