This review discusses the significant issue of fat infiltration in skeletal muscle, also known as myosteatosis, which is distinct from sarcopenia and is directly linked to declining muscle capacity. The article highlights the importance of understanding the triggers and regulatory mechanisms of fat infiltration to maintain skeletal muscle development and improve human health. Key triggers include aging, metabolic diseases, non-metabolic diseases, muscle injury, and other factors. The cellular origins of fat infiltration involve both myogenic and non-myogenic cells, with fibro/adipogenic progenitors (FAPs) being the primary source. The molecular regulatory mechanisms include signaling pathways such as Lkb1-AMPK, MAPK, Wnt/β-catenin, cAMP/PKA, hedgehog, and miRNAs. Detection methods for fat infiltration include imaging techniques like CT, pQCT, MRI, and QUS. Intervention strategies, such as exercise and nutritional interventions, are also discussed, with vitamin D, vitamin A, conjugated linoleic acid (CLA), linseed, and plant extracts showing potential benefits. The review emphasizes the complex nature of fat infiltration and the need for further research to develop effective therapeutic approaches.This review discusses the significant issue of fat infiltration in skeletal muscle, also known as myosteatosis, which is distinct from sarcopenia and is directly linked to declining muscle capacity. The article highlights the importance of understanding the triggers and regulatory mechanisms of fat infiltration to maintain skeletal muscle development and improve human health. Key triggers include aging, metabolic diseases, non-metabolic diseases, muscle injury, and other factors. The cellular origins of fat infiltration involve both myogenic and non-myogenic cells, with fibro/adipogenic progenitors (FAPs) being the primary source. The molecular regulatory mechanisms include signaling pathways such as Lkb1-AMPK, MAPK, Wnt/β-catenin, cAMP/PKA, hedgehog, and miRNAs. Detection methods for fat infiltration include imaging techniques like CT, pQCT, MRI, and QUS. Intervention strategies, such as exercise and nutritional interventions, are also discussed, with vitamin D, vitamin A, conjugated linoleic acid (CLA), linseed, and plant extracts showing potential benefits. The review emphasizes the complex nature of fat infiltration and the need for further research to develop effective therapeutic approaches.