The short answer
MASH — metabolic dysfunction-associated steatohepatitis — is the form of MASLD in which liver fat is accompanied by inflammation and liver-cell injury. It is the stage most closely linked with progressive scarring (fibrosis), and it is diagnosed on liver histology or inferred from a combination of clinical tests by a clinician.
What is happening?
Fat inside liver cells, combined with metabolic stress, can trigger cell injury (ballooning) and an inflammatory response.
Persistent inflammation activates repair pathways that lay down collagen — the process that leads to fibrosis.
Not everyone with liver fat develops MASH, and MASH does not follow a single fixed timeline.
Why does this matter?
Fibrosis stage, rather than the amount of fat, is the strongest predictor of liver-related outcomes in current evidence.
Identifying who may have inflammation and scarring is the reason clinicians use fibrosis scores and elastography rather than only an ultrasound report.
What does the evidence say?
Multiple longitudinal cohort studies and society guidance (AASLD, EASL) consistently identify advanced fibrosis as the dominant predictor of liver-related morbidity and mortality in MASLD/MASH.
Diagnosis of MASH remains histological in the strict sense; non-invasive tests estimate risk rather than confirm it.
Key takeaway
MASH is fatty liver with inflammation — and it is the stage where fibrosis assessment by a clinician becomes genuinely important.
Sources & references
American Association for the Study of Liver Diseases
AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease (2023) · Clinical guideline
View original sourceEASL, EASD and EASO
EASL–EASD–EASO Clinical Practice Guideline on MASLD (2024) · Clinical guideline
View original source
This page is general health education. It is not a diagnosis, and it cannot replace advice from your treating doctor. Never start or stop a prescribed medicine based on what you read here.
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