The concept of the biological embodiment of the environment—particularly the social environment—refers to the way in which the social becomes biological. Differential biological embodiment across social groups, in response to socially differentiated environments, could partly explain how the social gradient in health is constructed and, ultimately, how social health inequalities arise. A key question is how to measure the physiological reality or biological expression of this embodiment in humans. The concept of allostatic load (AL) refers to the idea of overall biological wear and tear resulting from adaptation to the environment via stress response systems. AL thus represents the price paid by the body over time to adapt to environmental demands. In practice, AL corresponds to a composite measure of various physiological systems. Findings from the literature, including our own studies based on British cohorts, show that AC is better at predicting future health than any of its constituent biomarkers taken separately, or than other composite scores such as metabolic syndrome. Studies on the social determinants of AC also reveal a social gradient of AC, which develops from childhood and continues throughout life. CA could therefore serve as a relevant proxy for the biological incorporation of environments, particularly social ones. Nevertheless, a number of issues warrant attention before CA can be operationalized in routine practice for public health interventions, particularly the validity of the systems and biomarkers used and the consideration of the dynamic nature of this measure.