There’s been talk of running tests on sweat instead of blood for many years. If memory serves I first came across the idea in 2010 (or thereabouts). Presumably, scientists have been working on a needlefree way to conduct tests longer that that.

A September 8, 2025 news item on Nanowerk announced a long awaited step forward, Note: A link has been removed,

A new wearable patch could one day replace certain blood tests with a quick check of sweat. A research team at KAIST has created a flexible sensor that attaches to the skin and continuously tracks changes in the body by analyzing sweat in real time (Nature Communications, “All-flexible chronoepifluidic nanoplasmonic patch for label-free metabolite profiling in sweat”).

The device, developed by Professor Ki-Hun Jeong and his team in the Department of Bio and Brain Engineering, overcomes a long-standing challenge in sweat-based health monitoring. Traditional methods struggled to collect sweat efficiently or required fluorescent tags to detect specific molecules. The new patch does both collection and analysis without added labels, making the process simpler and more precise.

Caption: <Figure 1. Flexible microfluidic nanoplasmonic patch (left). Sequential sample collection using the patch (center) and label-free metabolite profiling (right). In this study, we designed and fabricated a fully flexible nanoplasmonic microfluidic patch for label-free sweat analysis and performed SERS signal measurement and analysis directly from human sweat. Through this, we propose a platform capable of precisely identifying physiological changes induced by physical activity and dietary conditions.> Credit: KAIST

A September 8, 2025 The Korea Advanced Institute of Science and Technology (KAIST) press release (also on EurekAlert), formed the basis for the edited news item,

An era is opening where it’s possible to precisely assess the body’s health status using only sweat instead of blood tests. A KAIST research team has developed a smart patch that can precisely observe internal changes through sweat when simply attached to the body. This is expected to greatly contribute to the advancement of chronic disease management and personalized healthcare technologies.

KAIST (President Kwang Hyung Lee) announced on September 7th that a research team led by Professor Ki-Hun Jeong of the Department of Bio and Brain Engineering has developed a wearable sensor that can simultaneously and in real-time analyze multiple metabolites in sweat.

Recently, research on wearable sensors that analyze metabolites in sweat to monitor the human body’s precise physiological state has been actively pursued. However, conventional “label-based” sensors, which require fluorescent tags or staining, and “label-free” methods have faced difficulties in effectively collecting and controlling sweat. Because of this, there have been limitations in precisely observing metabolite changes over time in actual human subjects.

To overcome these limitations, the research team developed a thin and flexible wearable sweat patch that can be directly attached to the skin. This patch incorporates both microchannels for collecting sweat and an ultrafine nanoplasmonic structure* that label-freely analyzes sweat components using light. Thanks to this, multiple sweat metabolites can be simultaneously analyzed without the need for separate staining or labels, with just one patch application.

* Nanoplasmonic structure: An optical sensor structure where nanoscale metallic patterns interact with light, designed to sensitively detect the presence or changes in concentration of molecules in sweat.

The patch was created by combining nanophotonics technology, which manipulates light at the nanometer scale (one-hundred-thousandth the thickness of a human hair) to read molecular properties, with microfluidics technology, which precisely controls sweat in channels thinner than a hair.

In other words, within a single sweat patch, microfluidic technology enables sweat to be collected sequentially over time, allowing for the measurement of changes in various metabolites without any labeling process. Inside the patch are six to seventeen chambers (storage spaces), and sweat secreted during exercise flows along the microfluidic structures and fills each chamber in order.

The research team applied the patch to actual human subjects and succeeded in continuously tracking the changing components of sweat over time during exercise. Previously, only about two components could be checked simultaneously through a label-free approach, but in this study, they demonstrated for the first time in the world that three metabolites—uric acid, lactic acid, and tyrosine—can be quantitatively analyzed simultaneously, as well as how they change depending on exercise and diet. In particular, by using artificial intelligence analysis methods, they were able to accurately distinguish signals of desired substances even within the complex components of sweat.

Professor Ki-Hun Jeong said, “This research lays the foundation for precisely monitoring internal metabolic changes over time without blood sampling by combining nanophotonics and microfluidics technologies.” He added, “In the future, it can be expanded to diverse fields such as chronic disease management, drug response tracking, environmental exposure monitoring, and the discovery of next-generation biomarkers for metabolic diseases.”

…

Here’s a link to and a citation for the paper,

All-flexible chronoepifluidic nanoplasmonic patch for label-free metabolite profiling in sweat by Jaehun Jeon, Sangyeon Lee, Seongok Chae, Joo Hoon Lee, Hanjin Kim, Eun-Sil Yu, Hamin Na, Taejoon Kang, Hyung-Soon Park, Doheon Lee & Ki-Hun Jeong. Nature Communications volume 16, Article number: 8017 (2025) DOI: https://doi.org/10.1038/s41467-025-63510-2 Published: 27 August 2025 Version of record: 27 August 2025

This paper is open access.

I have another image featuring the ‘sweat patch’,

Caption: <Figure 2. Example of the fabricated patch worn (left) and images of sequential sweat collection and storage (right). By designing precise microfluidic channels based on capillary burst valves, sequential sweat collection was implemented, which enabled label-free analysis of metabolite changes associated with exercise and diet.> Credit: KAIST

Sometimes, the future looks very encouraging, indeed, for those don’t like blood tests. Although it could still be a while, the most recent previous story here on sweat, health monitoring, and microfluidics was in a May 20, 2015 posting titled “A ‘sweat’mometer—sensing your health through your sweat.”