**Background:** This article investigates biological clocks, technologies that measure biological age using molecular biomarkers such as epigenomics, proteomics, metabolomics, and glycomics. The authors situate biological clocks within the broader agenda of personalized medicine, which aims to tailor diagnostics and therapeutics to individual characteristics. While biological clocks promise personalized assessments of aging, the authors note that little is known about how these technologies are actually developed and commercialized. The paper draws on the concept of 'decay' as an analytical framework to examine how norms about aging tempo are constructed and how responsibility for managing bodily decay is assigned.
**Methods:** The study is based on ethnographic fieldwork conducted by the first author at two sites: the Wilson Lab, an academic research laboratory in Scotland that manages a cohort database of healthy volunteers from the Northern Isles of Scotland, and Genos, a biotechnology company in Croatia specializing in glycomics analysis. Fieldwork occurred in October 2019 at Genos and February 2020 at the Wilson Lab, involving participant observation of data practices, laboratory work, meetings, and seminars. The first author conducted 19 in-depth semi-structured interviews (7 at Genos, 12 at the Wilson Lab). All informants were pseudonymized. Data were coded using network thematic analysis. The authors also analyzed promotional materials from the GlycanAge website.
**Key Results:** The authors present three main findings. First, in the laboratory setting, biological clocks are built using population data to establish a 'baseline' norm of biological decay. At the Wilson Lab, PhD student Anna used nine different omics technologies to build clocks, focusing exclusively on molecular markers while bracketing environmental and socioeconomic factors. At Genos, the baseline for GlycanAge was derived from glycomics data from approximately 100,000 individuals, with separate baselines developed according to sex and ethnicity—driven partly by commercial considerations to serve global markets. In both labs, aging is conceptualized as endo-decay (internal, molecular processes), following an inevitable, unidirectional trajectory from birth to death. Second, when biological clocks are commercialized as direct-to-consumer products, the framing shifts. GlycanAge is marketed as a wellness test (not a diagnostic test) costing 350 euros, targeting customers 'mostly over 40' in the 'upper spending bracket.' The test reframes aging as exo-decay—malleable and controllable through individual lifestyle changes such as diet, exercise, and stress management. The GlycanAge website features customer stories showing individuals reducing their biological age (e.g., from 45 to 28 over 2.5 years). Third, the maintenance work promoted is a commodified form of self-care: customers are urged to take regular tests (subscription model), consult with 'Lifestyle Medicine doctors,' nutritionists, and personal trainers, and experiment with lifestyle changes to optimize their biological age. The authors note that the health advice resembles general healthy lifestyle recommendations, raising questions about the necessity of individualization via biological clocks.
**Clinical Implications:** The authors argue that biological clocks enact a 'politics of decay' by making particular forms of decay visible while rendering others invisible. Specifically, the technologies decontextualize aging from socioeconomic determinants (the 'causes of the causes') and place responsibility for managing decay on individual consumers. This creates a form of 'ground-state prevention'—a life-long preoccupation with optimizing biological age regardless of admitted uncertainties about what is measured. The authors caution that this approach primarily benefits already healthy, wealthy individuals in the Global North, potentially excluding those who cannot afford the test (350 euros) or lack resources to follow health recommendations. The paper concludes that biological clocks are not neutral scientific facts but performative technologies that shape how aging and health are understood, with significant ethical implications for who is deemed responsible for aging and who is left out.