These days, many people are able to answer this question at the drop of a hat \u2013 all it takes is a quick glance at their smartphone. More often than not, our smartphones have a pedometer app pre-installed, while fitness trackers and smartwatches have become ubiquitous. These technologies, also known as wearables<\/strong>, have simplified the transition to digital health monitoring [1]. For many users, however, a step count alone is not enough. In addition, heart rate, training intensity or sleep quality are recorded. For the first time, this renders subjective variables such as effort, stress or fatigue constantly measurable and comparable [1]. <\/p>\n\n The ability to constantly monitor physiological and biochemical parameters is one of the key developments in modern medical technology. What once began with intermittent blood glucose readings is evolving into integrated systems of biosensors worn against the skin, which record a range of biomarkers virtually in real time [2,3]. This type of diagnosis and treatment monitoring marks a paradigm shift from reactive medicine to preventative, personalised medicine [3].<\/mark> <\/p>\n\n The term wearables describes electronic devices worn on the body to continuously record health and fitness data [4]. Among the best known applications are smartwatches <\/strong>and fitness trackers<\/strong>, which record and evaluate data and in many cases further process this data via mobile end devices. Transmission is generally wireless, such as via Bluetooth [4]. <\/p>\n\n In recent years, the range of applications for wearables has expanded enormously. For some time now, modern devices have been monitoring much more than just activity data such as step count or heart rate, with more and more models able to track physiological and biochemical parameters. These include oxygen saturation of the blood, the glucose level of interstitial fluid as well as lactate and electrolyte concentrations in sweat or tissue [3,5]. This development is primarily the result of advances in sensor technology and material sciences [6]. <\/p>\n\n New-generation wearables<\/strong> \u2013 including skin-based sensor patches, electronic tattoos<\/strong> or sensor-integrated respiratory masks <\/strong>\u2013 are opening up new avenues for diagnosis. Depending on the type of wearable, markers of metabolic processes or disease progression can be continuously monitored [3]. Early-stage studies are also investigating the continuous tracking of drug levels, which could be particularly significant for patients with chronic illnesses, since wearables offer a non-invasive or minimally invasive means of data capture and help to optimise therapy processes, to improve treatment adherence and reduce potential hospital stays [4,6]. <\/p>\n\n At the beating heart of modern wearables lies integrated biosensor technology: a biosensor is, simply put, an analytical system that detects specific substances in the body or in biological fluids.<\/mark> Examples include glucose in cases of diabetes, lactate as a marker of physical strain, electrolytes such as sodium or potassium or even hormones such as cortisol; current research is still exploring how the latter can be reliably measured. Biosensors use biological identifiers, such as enzymes or antibodies, which interact a certain way with a specific substance [2,7]. The resulting chemical reaction is converted into a measurable electrical or optical signal by means of a transducer [2]. This allows for concentrations of biomarkers, such as glucose, lactate or electrolytes to be quantified [2]. <\/p>\n\n The combination of biosensors, microelectronics and wearable technology facilitates the continuous monitoring of vital functions and biochemical parameters [2,3]. <\/mark>Flexible sensor systems integrated into the user\u2019s skin mechanically adjust to the body and can be worn for longer periods [2]. Advances in material science, such as with conductive polymers and nanostructured materials, have been instrumental in enhancing the sensitivity and selectivity of these systems [2,3]. <\/p>\n\n One highly promising approach lies in the use of sweat as a diagnostic medium. Sweat contains numerous biomarkers, including electrolytes, metabolites and \u2013 to a limited extent \u2013 even hormonal signals [5]. Wearable sensors can continuously record these substances in order to provide a dynamic picture of physiological processes, which goes beyond that of on-the-spot laboratory analyses. Alongside this development, the analysis of interstitial fluid is becoming increasingly significant. This is closely interlinked with the blood and provides the basis for established applications, such as continuous glucose measurement [3]. Cutting-edge microneedle based systems offer minimally invasive access to this compartment and widen the opportunities for biomarker detection greatly<\/mark> [3]. <\/p>\n\n The integration of multiple sensors into one system constitutes a further step in development. Such multi-biomarker platforms allow for simultaneous monitoring of various parameters and open up new opportunities for individualised diagnosis [8]. <\/p>\n\n Central to this is the digital processing of the data collected. Machine learning and artificial intelligence allow for large volumes of data to be evaluated and individual patterns to be identified. This provides a basis for developing early warning systems, which are quick to identify deviations from the physiological normal state and support preventive measures [3]. <\/p>\n\n The possible applications extend beyond classical medicine. In sports science, for instance, wearables can help to optimise training processes, in occupational medicine, it assists with the monitoring of physical strain. In space medicine too, continuously operational monitoring systems are increasingly important, because they facilitate the remote monitoring of the astronauts\u2019 health, while subject to extreme conditions. Parallel to this, there are still challenges to be overcome. These include ensuring the quality and comparability of the collected data, the long-term stability of the sensors and the standardisation of measurement techniques. Last but not least, it is crucial that sensitive health data is protected [2,3]. <\/p>\n\n Further to this: the clinical integration of wearables is subject to strict regulatory requirements. While many systems are established in the consumer sector, their use in the field of medical care requires extensive validation studies [1]. As such, the transition to clinical practice calls for close collaboration between research, industry and healthcare. Despite all the challenges still to be overcome, it is conceivable that wearables and skin-based biosensors are on the brink of transitioning from technology to application. They make health measurable, comparable and \u2013 in some cases \u2013 predictable. This fundamentally shifts the focus of medicine: from the treatment of disease to the active control of health. <\/mark><\/p>\n\n Sources:<\/strong><\/p>\n\n [1] Fraunhofer-Institut f\u00fcr Elektronische Mikrosysteme und Festk\u00f6rper-Technologien (EMFT). Fr\u00fchzeitige Krankheitsdiagnose mit medizinischen Wearables [Internet]. [2] Suryaprabha T et al. Smart wearable and implantable biosensors for continuous health monitoring: materials, biocompatibility, and AI integration. npj Flexible Electronics. 2026;10:46. doi:10.1038\/s41528-026-00560-6. <\/p>\n\n [3] Ray TR et al. Bio-integrated wearable systems: a comprehensive review. Chemical Reviews. 2019;119:5461\u20135533. doi:10.1021\/acs.chemrev.8b00573. <\/p>\n\n [4] Dincer C und Ates C. Wearables \u2013 Nachweis von Biomarkern mithilfe nicht-invasiver Gesundheits\u00fcberwachung. Sport\u00e4rztezeitung [Internet]. 2025. [5] Rind S et al. Sweat-based wearable biosensors: A new era of continuous, noninvasive health monitoring and diagnostics. Wearable Electronics. 2025;2:323\u2013343. doi:10.1016\/j.wees.2025.08.002. <\/p>\n\n [6] Deutsche Gesellschaft f\u00fcr Biomedizinische Technik (DGBMT). Wie Wearables und Biosensoren unsere Gesundheit \u00fcberwachen und verbessern [Internet]. From recreational to medical application<\/h3>\n\n
Biosensors as the key to success<\/h3>\n\n
Sweat and interstitial fluid as diagnostic media<\/h3>\n\n
Opportunities and challenges<\/h3>\n\n
Regulatory requirements and outlook<\/h3>\n\n
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