Background. Obesity among Generation Z (born 1997–2012) has emerged as a critical public health crisis in urban India. Existing research remains fragmented, focusing on isolated determinants. This study addresses that gap by adopting a multi-domain hygiene model to empirically investigate obesity prevalence and its behavioural determinants. Methods. A quantitative, descriptive, cross-sectional survey design was employed. Primary data were collected from 95 urban Generation Z respondents aged 18–28 years in Tirupati, Andhra Pradesh, using a structured 27-item questionnaire. Composite hygiene domain scores were constructed and seven inferential statistical tests applied at α = 0.05 using Python (scipy.stats, pandas). Results. The sample mean BMI was 27.71 kg/m² (SD = 8.63), with 46.3% of respondents classified as overweight (32.6%) or obese (13.7%). Dietary hygiene emerged as the strongest predictor of BMI (r = 0.44, p < 0.001). Psychological stress was positively correlated with BMI (r = 0.32, p = 0.001). Physical activity differed dramatically across weight groups (F = 52.48, p < 0.001). Sleep duration showed the most categorical discriminatory power (χ² = 43.84, p < 0.001): no respondent sleeping fewer than 6 hours maintained Normal weight status. Conclusion. Obesity in Gen Z is a multifactorial metabolic outcome. Integrated, multi-domain behavioural interventions targeting sleep, diet, physical activity, and psychological stress simultaneously are essential for effective obesity prevention in this population.