A new ultrathin, compliant skin-like sensor/actuator technology is introduced for precise and continuous thermal characterization of human skin. This technology can pliably laminate onto the epidermis to provide continuous, accurate thermal characterizations that are unavailable with other methods. Examples include non-invasive spatial mapping of skin temperature with millikelvin precision and simultaneous quantitative assessment of tissue thermal conductivity. The devices can also be implemented in ways that reveal the time-dynamic influence of blood flow and perfusion on these properties. Experimental and theoretical studies establish the underlying principles of operation and define engineering guidelines for device design. Evaluation of subtle variations in skin temperature associated with mental activity, physical stimulation, and vasoconstriction/dilation, along with accurate determination of skin hydration through measurements of thermal conductivity, represent some important operational examples. Traditional methods for skin thermography use either sophisticated infrared digital cameras for spatial imaging or simple, paste-on temperature sensors for single-point measurements. These and other related technologies have value in certain contexts, but they do not offer continuous, cost-effective precision mapping capabilities required for use at the point of care. For example, infrared cameras provide millikelvin precision and fine resolution in imaging, but they are expensive and require immobilization of the patient. Point contact sensors avoid these limitations, but they do not have the ability to perform spatial mapping, as typically required to extract meaningful information across the structurally and functionally heterogeneous surface of the skin. Such devices also irritate the skin and modify its natural physiological responses by thermally and mechanically loading its surface. The introduced technology combines precision measurement with mapping capabilities in a form that integrates intimately and non-invasively onto the surface of the skin. The devices incorporate microscale temperature sensors that can simultaneously act as micro-heaters (actuators) in arrayed layouts on thin, low modulus elastic sheets. The sensors/actuators rely on either thin serpentine features of thin metal (50 nm thick; Au) or PIN diodes constructed with nanoscale membranes of silicon (320 nm thick; Si nanomembranes). Integrated collections of such components offer mechanical properties and geometries matched to human tissue through advanced application of emerging concepts in stretchable electronics. A key enabling characteristic for use on the skin is the ability to provide soft, conformal contact with the epidermis in a manner that does not constrain or alter natural motions or behaviours. This epidermal design enables robust adhesion with minimal irritation or discomfort, and without measurement artefacts that can arise from relative motion of the sensors/actuators and the skin or from interference with processes such as transdermal water loss. The devices are typically applied to skin that is mostly hairless (glabrous) or shaved. Small amounts of hair can be accommodated. A thin, flexible, conductive cable establishes connection to external control and data acquisition electronics. Typical measurements involve averaged outputs sampled at 2 or 0.5 Hz, yieldingA new ultrathin, compliant skin-like sensor/actuator technology is introduced for precise and continuous thermal characterization of human skin. This technology can pliably laminate onto the epidermis to provide continuous, accurate thermal characterizations that are unavailable with other methods. Examples include non-invasive spatial mapping of skin temperature with millikelvin precision and simultaneous quantitative assessment of tissue thermal conductivity. The devices can also be implemented in ways that reveal the time-dynamic influence of blood flow and perfusion on these properties. Experimental and theoretical studies establish the underlying principles of operation and define engineering guidelines for device design. Evaluation of subtle variations in skin temperature associated with mental activity, physical stimulation, and vasoconstriction/dilation, along with accurate determination of skin hydration through measurements of thermal conductivity, represent some important operational examples. Traditional methods for skin thermography use either sophisticated infrared digital cameras for spatial imaging or simple, paste-on temperature sensors for single-point measurements. These and other related technologies have value in certain contexts, but they do not offer continuous, cost-effective precision mapping capabilities required for use at the point of care. For example, infrared cameras provide millikelvin precision and fine resolution in imaging, but they are expensive and require immobilization of the patient. Point contact sensors avoid these limitations, but they do not have the ability to perform spatial mapping, as typically required to extract meaningful information across the structurally and functionally heterogeneous surface of the skin. Such devices also irritate the skin and modify its natural physiological responses by thermally and mechanically loading its surface. The introduced technology combines precision measurement with mapping capabilities in a form that integrates intimately and non-invasively onto the surface of the skin. The devices incorporate microscale temperature sensors that can simultaneously act as micro-heaters (actuators) in arrayed layouts on thin, low modulus elastic sheets. The sensors/actuators rely on either thin serpentine features of thin metal (50 nm thick; Au) or PIN diodes constructed with nanoscale membranes of silicon (320 nm thick; Si nanomembranes). Integrated collections of such components offer mechanical properties and geometries matched to human tissue through advanced application of emerging concepts in stretchable electronics. A key enabling characteristic for use on the skin is the ability to provide soft, conformal contact with the epidermis in a manner that does not constrain or alter natural motions or behaviours. This epidermal design enables robust adhesion with minimal irritation or discomfort, and without measurement artefacts that can arise from relative motion of the sensors/actuators and the skin or from interference with processes such as transdermal water loss. The devices are typically applied to skin that is mostly hairless (glabrous) or shaved. Small amounts of hair can be accommodated. A thin, flexible, conductive cable establishes connection to external control and data acquisition electronics. Typical measurements involve averaged outputs sampled at 2 or 0.5 Hz, yielding