###### Abstract  
Aflatoxin M1 (AFM1), a toxic metabolite of aflatoxin B1 (AFB1), is commonly found in cow's milk (CM) when dairy cattle consume contaminated feed. Chronic exposure to AFM1 poses serious health risks, particularly for children. This study aimed to quantify AFM1 levels in commercial CM available in Mexico and assess the associated carcinogenic risk across six age groups. A total of 23 milk samples were collected between March and July 2023 from supermarkets and convenience stores. AFM1 was measured using high-performance liquid chromatography (HPLC). Estimated daily intake (EDI), carcinogenic risk index (CRI), and Monte Carlo simulations (MCS) to model exposure were employed. AFM1 was detected in all samples, with 80% exceeding the legal limits set by Mexican and European regulations. The highest CRI values were observed in children aged 1-4 years (CRI \(>5\times 10^{3}\)), indicating an elevated risk. There were no statistically significant differences in AFM1 concentration among different milk or thermal treatments. A cluster analysis revealed patterns related to AFM1 content, price, and processing methods. The widespread detection of AFM1 raises a public health concern, especially for vulnerable populations. This underscores the need for targeted regulatory strategies and improved control of aflat in the dairy production chain. affatoxin M1]Aflatoxin M1 Levels in Commercial Cows' Milk in Contamination and Carcinogenic Risk Assessment [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 111, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 12 measures significantly contribute to the contamination of animal feed with AFB1, particularly in tropical and subtropical regions [5; 6]. The AFM1 is excreted into milk and dairy products, where it can persist despite pasteurization and ultra-high temperature (UHT) treatments [7; 8]. AFM1 has been classified by the International Agency for Research on Cancer (IARC) as a Group 1 human carcinogen, attributed to its genotoxic, immunosuppressive, and mutagenic properties [3]. Chronic exposure to AFM1 is associated with an elevated risk of hepatocellular carcinoma, particularly among populations with high consumption of milk and limited dietary diversity [9; 10]. A significant inverse correlation has been established between the risk of carcinogenicity and body weight, particularly among children from birth to 26 months of age in Nepal who were chronically exposed to aflat. This reinforces that lower body mass predisposes individuals to a higher relative exposure [11]. Evidence suggests that the toxic effects of AFM1 are more pronounced in pediatric populations than adults, attributable to their lower body weight, greater milk consumption, and the development of physiological systems with limited capacity to metabolize and excrete toxins [10; 12; 13]. Prolonged exposure to AFM1 during the early years of life has been associated with hepatocellular damage, immunosuppression, altered nutrient absorption, and growth retardation [14; 15]. Furthermore, even low-dose exposure may impede protein synthesis and liver enzyme functionality, potentially leading to long-term developmental disorders [16; 17]. The presence of AFM1 in milk and dairy products has been widely reported in several countries using various analytical approaches. In Greece, [PERSON] et al. (2021) compared commercial enzyme-linked immunosorbent assay kits with a high-performance liquid chromatography with fluorescence detection (HPLC-FLD) method developed to analyze AFM1 in raw milk, underlining the importance of selecting context-specific analytical procedures [18].