Elevations in sweat sodium concentration following ischemia-reperfusion injury during passive heat stress.

Renal ischemia-reperfusion (I/R) injury results in damage to the renal tubules and causes impairments in sodium [Na+] reabsorption. Given the inability to conduct mechanistic renal I/R injury studies in vivo in humans, eccrine sweat glands have been proposed as a surrogate model given the anatomical and physiological similarities. We tested the hypothesis that sweat Na+ concentration is elevated following I/R injury during passive heat stress. We also tested the hypothesis that I/R injury during heat stress will impair cutaneous microvascular function. Fifteen young healthy adults completed ∼160 min of passive heat stress using a water-perfused suit (50°C). At 60 min of whole body heating, one upper arm was occluded for 20 min followed by a 20-min reperfusion. Sweat was collected from each forearm via an absorbent patch pre- and post-I/R. Following the 20-min reperfusion, cutaneous microvascular function was measured via local heating protocol. Cutaneous vascular conductance (CVC) was calculated as red blood cell flux/mean arterial pressure and normalized to CVC during local heating to 44°C. Na+ concentration was log-transformed and data were reported as a mean change from pre-I/R (95% confidence interval). Changes in sweat sodium concentration from pre-I/R differed between arms post-I/R (experimental arm: +0.97 [+0.67 - 1.27] [LOG] Na+; control arm: +0.68 [+0.38 - 0.99] [LOG] Na+; P < 0.01). However, CVC during the local heating was not different between the experimental (80 ± 10%max) and control arms (78 ± 10%max; P = 0.59). In support of our hypothesis, Na+ concentration was elevated following I/R injury, but likely not accompanied by alterations in cutaneous microvascular function.NEW & NOTEWORTHY In the present study, we have demonstrated that sweat sodium concentration is elevated following ischemia-reperfusion injury during passive heat stress. This does not appear to be mediated by reductions in cutaneous microvascular function or active sweat glands, but may be related to alterations in local sweating responses during heat stress. This study demonstrates a potential use of eccrine sweat glands to understand sodium handling following ischemia-reperfusion injury, particularly given the challenges of in vivo studies of renal ischemia-reperfusion injury in humans.

Sweat as a diagnostic biofluid.

Skin-interfaced microfluidic systems help assess health status and chemical exposure.

A Simple Non-Contact Optical Method to Quantify In-Vivo Sweat Gland Activity and Pulsation.

OBJECTIVE: Most methods for monitoring sweat gland activity use simple gravimetric methods, which merely measure the average sweat rate of multiple sweat glands over a region of skin. It would be extremely useful to have a method which could quantify individual gland activity in order to improve the treatment of conditions which use sweat tests as a diagnostic tool, such as hyperhidrosis, cystic fibrosis, and peripheral nerve degeneration. METHODS: An optical method using an infrared camera to monitor the skin surface temperature was developed. A thermodynamics computer model was then implemented to utilize these skin temperature values along with other environmental parameters, such as ambient temperature and relative humidity, to calculate the sweat rates of individual glands using chemically stimulated and unstimulated sweating. The optical method was also used to monitor sweat pulsation patterns of individual sweat glands. RESULTS: In this preliminary study, the feasibility of the optical approach was demonstrated by measuring sweat rates of individual glands at various bodily locations. Calculated values from this method agree with expected sweat rates given values found in literature. In addition, a lack of pulsatile sweat expulsion was observed during chemically stimulated sweating, and a potential explanation for this phenomenon was proposed. CONCLUSION: A simple, non-contact optical method to quantify sweat gland activity in-vivo was presented. SIGNIFICANCE: This method allows researchers and clinicians to investigate several sweat glands simultaneously, which has the potential to provide more accurate diagnoses and treatment as well as increase the potential utility for wearable sweat sensors.

Screen-Printed Carbon Black/Recycled Sericin@Fabrics for Wearable Sensors to Monitor Sweat Loss.

Wearable sensors to monitor human sweat loss are important for real-time health monitoring, requiring electrically conductive, mechanically flexible fabrics as working electrodes. Here, a textile-based sweat monitor was fabricated by screen printing of carbon black and recycled sericin on cotton fabrics. The obtained fabric with excellent flexibility, good hydrophilicity (86°), and proper resistivity (61.7 Ω/cm2) can be used as a working electrode for a wearable sweat monitor. A wearable sweat monitor is highly sensitive (42.7% in acidic sweat), flexible, and can be washed (99.1% retention after 30 washes). This work offers a promising approach for the fabrication of wearable sensors and promotes the widespread applications of personalized health-monitoring devices.

A Rare Case of Blood & Sweat: Hematohidrosis.

Hematohidrosis is an uncommon pathophysiological condition of sweating blood. A young lady with abrupt bleeding from the skin (since January 2017) was brought to the emergency. The bleeding was vanished after mopping with no site of injury, but it reappeared soon enough confirming its nature. Bleeding time (BT), clotting time (CT), and the prothrombin time (PT) was within normal limit. This patient is confirmed as a case of hematohidrosis by the method of exclusion and the presence of blood was finalized by benzidine test as well as biochemical and microscopic examination of it. Now, no treatment is available as per the latest pieces of evidence. Also, the cause of it is not known till date. Psychological anxiety is a predisposing cause for hematohidrosis.

Preparation of green and sustainable colorimetric cotton assay using natural anthocyanins for sweat sensing.

Herein, we develop a novel smart cotton swab as a diagnostic assay for onsite monitoring of sweat pH changes toward potential applications in monitoring human healthcare and drug exam. Anthocyanin (Ac) can be extracted from Brassica oleracea var. capitata f. rubra using a simple procedure. Then, it can be used as a direct dye into cotton fibers using potash alum as mordant (M) to fix the anthocyanin dye onto the surface of the cotton fabric (Cot). This was monitored by generating mordant/anthocyanin nanoparticles (MAcNPs) onto the fabric surface. The cotton sensor assay demonstrated colorimetric changes in the ultraviolet-visible absorbance spectral analysis associated with a blueshift from 588 to 422 nm with increasing the pH of a perspiration simulant fluid. The biochromic performance of the dyed cotton diagnostic assay depended essentially on the halochromic activity of the anthocyanin spectroscopic probe to demonstrate a color change from pink to green due to intramolecular charge transfer occurring on the anthocyanin chromophore. After dyeing, no significant defects were detected in air-permeability and bend length. High colorfastness was investigated for the dyed cotton fabrics.

Age-related mushroom body expansion in male sweat bees and bumble bees.

A well-documented phenomenon among social insects is that brain changes occur prior to or at the onset of certain experiences, potentially serving to prime the brain for specific tasks. This insight comes almost exclusively from studies considering developmental maturation in females. As a result, it is unclear whether age-related brain plasticity is consistent across sexes, and to what extent developmental patterns differ. Using confocal microscopy and volumetric analyses, we investigated age-related brain changes coinciding with sexual maturation in the males of the facultatively eusocial sweat bee, Megalopta genalis, and the obligately eusocial bumble bee, Bombus impatiens. We compared volumetric measurements between newly eclosed and reproductively mature males kept isolated in the lab. We found expansion of the mushroom bodies-brain regions associated with learning and memory-with maturation, which were consistent across both species. This age-related plasticity may, therefore, play a functionally-relevant role in preparing male bees for mating, and suggests that developmentally-driven neural restructuring can occur in males, even in species where it is absent in females.

A non-printed integrated-circuit textile for wireless theranostics.

While the printed circuit board (PCB) has been widely considered as the building block of integrated electronics, the world is switching to pursue new ways of merging integrated electronic circuits with textiles to create flexible and wearable devices. Herein, as an alternative for PCB, we described a non-printed integrated-circuit textile (NIT) for biomedical and theranostic application via a weaving method. All the devices are built as fibers or interlaced nodes and woven into a deformable textile integrated circuit. Built on an electrochemical gating principle, the fiber-woven-type transistors exhibit superior bending or stretching robustness, and were woven as a textile logical computing module to distinguish different emergencies. A fiber-type sweat sensor was woven with strain and light sensors fibers for simultaneously monitoring body health and the environment. With a photo-rechargeable energy textile based on a detailed power consumption analysis, the woven circuit textile is completely self-powered and capable of both wireless biomedical monitoring and early warning. The NIT could be used as a 24/7 private AI "nurse" for routine healthcare, diabetes monitoring, or emergencies such as hypoglycemia, metabolic alkalosis, and even COVID-19 patient care, a potential future on-body AI hardware and possibly a forerunner to fabric-like computers.

A wearable patch for continuous analysis of thermoregulatory sweat at rest.

The body naturally and continuously secretes sweat for thermoregulation during sedentary and routine activities at rates that can reflect underlying health conditions, including nerve damage, autonomic and metabolic disorders, and chronic stress. However, low secretion rates and evaporation pose challenges for collecting resting thermoregulatory sweat for non-invasive analysis of body physiology. Here we present wearable patches for continuous sweat monitoring at rest, using microfluidics to combat evaporation and enable selective monitoring of secretion rate. We integrate hydrophilic fillers for rapid sweat uptake into the sensing channel, reducing required sweat accumulation time towards real-time measurement. Along with sweat rate sensors, we integrate electrochemical sensors for pH, Cl-, and levodopa monitoring. We demonstrate patch functionality for dynamic sweat analysis related to routine activities, stress events, hypoglycemia-induced sweating, and Parkinson's disease. By enabling sweat analysis compatible with sedentary, routine, and daily activities, these patches enable continuous, autonomous monitoring of body physiology at rest.

The sweat glands' maximum ion reabsorption rates following heat acclimation in healthy older adults.

NEW FINDINGS: What is the central question to this study? Do the sweat glands' maximum ion reabsorption rates increase following heat acclimation in healthy older individuals and is this associated with elevated aldosterone concentrations? What is the main finding and its importance? Sweat gland maximum ion reabsorption rates improved heterogeneously across body sites, which occurred without any changes in aldosterone concentration following a controlled hyperthermic heat acclimation protocol in healthy older individuals. ABSTRACT: We examined whether the eccrine sweat glands' ion reabsorption rates improved following heat acclimation (HA) in older individuals. Ten healthy older adults (>65 years) completed a controlled hyperthermic (+0.9°C rectal temperature, Tre ) HA protocol for nine non-consecutive days. Participants completed a passive heat stress test (lower leg 42°C water submersion) pre-HA and post-HA to assess physiological regulation of sweat gland ion reabsorption at the chest, forearm and thigh. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate (SR). We explored the responses again after a 7-day decay. During passive heating, the Tb thresholds for sweat onset on the chest and forearm were lowered after HA (P < 0.05). However, sweat sensitivity (i.e. the slope), the SR at a given Tre and gross sweat loss did not improve after HA (P > 0.05). Any changes observed were lost during the decay. Pilocarpine-induced sudomotor responses to iontophoresis did not change after HA (P ≥ 0.801). Maximum ion reabsorption rate was only enhanced at the chest (P = 0.001) despite unaltered aldosterone concentration after HA. The data suggest that this adaptation is lost after 7 days' decay. The HA protocol employed in the present study induced partial adaptive sudomotor responses. Eccrine sweat gland ion reabsorption rates improved heterogeneously across the skin sites. It is likely that aldosterone secretion did not alter the chest sweat ion reabsorption rates observed in the older adults.

Sweat rate and environmental factors in junior Laser class sailors / Tasa de sudoración y factores ambientales en regatistas juveniles de clase Láser

INTRODUCTION: Recent studies have reported differences in sweat rate (SR) in laser class (LC) sailors under extreme environ-mental conditions (EC). This study aimed to determine a 'standard-like' SR in junior Laser 4.7 sailors under 'not-extreme' weather conditions to achieve an adequate fluid replacement rate for training and racing sessions. Additionally, we analysed the hypothetical relationship between SR and certain environmental factors, not just considering them as independent variables, but also including them as a whole factor, usually known as 'windchill' (WCh). MATERIAL AND METHOD: Nine male elite junior Laser 4.7 class athletes were included in this descriptive study. They were monitored during the entire year of training and racing sessions, including national and international championships. Body mass changes as well as their food and fluid intake were measured for each sailor before and after sailing to estimate SR, absolute body mass change, and percentage body mass variation for all the sessions. Athletes were asked to maintain "ab libitum" fluid and food intake during the study. Environmental temperature, wind speed, and relative humidity were measured. RESULTS: Significant differences (p = 0.012) were observed between training and racing sessions with respect to SR, 0.18 (± 0.14) L.h-1vs. 0.23 (± 0.12 L.h-1). Environmental temperature and WCh during racing showed an inverse relationship with SR. DISCUSSION: This result suggests that increased fluid and food intake are required under cold weather conditions to maintain the 'target' weight during the competitions and improve performance

INTRODUCCIÓN: Recientemente, algunos estudios han reportado diferencias en la tasa de sudoración (SR) en regatistas de clase láser (LC) bajo condiciones ambientales (EC) extremas. Este estudio pretende determinar una especie de "SR standard" en regatistas juveniles de Láser 4.7 bajo condiciones "no extremas", con el objetivo de alcanzar una adecuada reposición de líquidos tanto para entrenamientos como en competición. Adicionalmente, se ha analizado una hipotética relación entre SR y los factores ambientales, considerándolos no únicamente como variables independientes, sino también como una variable compleja, conocida habitualmente como "sensación térmica" (WCh). MATERIAL Y MÉTODO: Nueve regatistas juveniles de Láser 4.7 han participado en este estudio descriptivo y prospectivo. Todos ellos han sido monitorizados durante todo un año de sesiones de entrenamiento y competición, incluyendo regatas nacionales como internacionales. Los cambios en la masa corporal, así como la ingesta de líquidos y sólidos han sido registrados de forma individual para cada regatista, antes y después de cada sesión para estimar la SR, los cambios totales en la masa corporal, así como las variaciones en el porcentaje de masa corporal. Se instó a los regatistas a ingerir comida y bebida "ab libidtum" a lo largo del estudio. La temperatura ambiental, la intensidad de viento y la humedad relativa fueron registradas. RESULTADOS: Se observaron diferencias significativas (p = 0,012) para la SR entre los entrenos y las competiciones 0,18 (± 0,14) L.h-1vs. 0,23 (± 0,12 L.h-1). La temperatura ambiental y la WCh durante las competiciones mostraron además una relación inversa con la SR. DISCUSIÓN: Estos resultados sugieren que una mayor ingesta de líquidos y sólidos bajo condiciones de "frío ambiental" es necesaria para mantener el peso ideal, mejorando así el rendimiento durante la competición

Encoding fear intensity in human sweat.

Humans, like other animals, have an excellent sense of smell that can serve social communication. Although ample research has shown that body odours can convey transient emotions like fear, these studies have exclusively treated emotions as categorical, neglecting the question whether emotion quantity can be expressed chemically. Using a unique combination of methods and techniques, we explored a dose-response function: Can experienced fear intensity be encoded in fear sweat? Specifically, fear experience was quantified using multivariate pattern classification (combining physiological data and subjective feelings with partial least-squares-discriminant analysis), whereas a photo-ionization detector quantified volatile molecules in sweat. Thirty-six male participants donated sweat while watching scary film clips and control (calming) film clips. Both traditional univariate and novel multivariate analysis (100% classification accuracy; Q2: 0.76; R2: 0.79) underlined effective fear induction. Using their regression-weighted scores, participants were assigned significantly above chance (83% > 33%) to fear intensity categories (low-medium-high). Notably, the high fear group (n = 12) produced higher doses of armpit sweat, and greater doses of fear sweat emitted more volatile molecules (n = 3). This study brings new evidence to show that fear intensity is encoded in sweat (dose-response function), opening a field that examines intensity coding and decoding of other chemically communicable states/traits. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Towards Wearable and Flexible Sensors and Circuits Integration for Stress Monitoring.

Excessive stress is one of the main causes of mental illness. Long-term exposure of stress could affect one's physiological wellbeing (such as hypertension) and psychological condition (such as depression). Multisensory information such as heart rate variability (HRV) and pH can provide suitable information about mental and physical stress. This paper proposes a novel approach for stress condition monitoring using disposable flexible sensors. By integrating flexible amplifiers with a commercially available flexible polyvinylidene difluoride (PVDF) mechanical deformation sensor and a pH-type chemical sensor, the proposed system can detect arterial pulses from the neck and pH levels from sweat located in the back of the body. The system uses organic thin film transistor (OTFT)-based signal amplification front-end circuits with modifications to accommodate the dynamic signal ranges obtained from the sensors. The OTFTs were manufactured on a low-cost flexible polyethylene naphthalate (PEN) substrate using a coater capable of Roll-to-Roll (R2R) deposition. The proposed system can capture physiological indicators with data interrogated by Near Field Communication (NFC). The device has been successfully tested with healthy subjects, demonstrating its feasibility for real-time stress monitoring.

Perspiration interventions for conservative management of kidney disease and uremia.

PURPOSE OF REVIEW: There has been an increasing interest in developing novel technologies to treat patients with chronic kidney disease as evidenced by KidneyX, the public-private partnership between government and industry. Perhaps a simple technology for treating kidney failure would be to utilize perspiration. It is a physiological process, and when used properly it might not be an unpleasant experience. This review will explore the current state of knowledge regarding perspiration therapy in the setting of far advanced kidney failure. RECENT FINDINGS: A literature review using the PubMed database was conducted between 1 April 2019 and 3 September 2019. Search terms are shown in Table 1. Major themes of the results include diaphoresis therapy for patients with chronic kidney disease, excessive perspiration causing kidney disease, analysis of sweat to diagnose cystic fibrosis, and analysis of sweat to replenish lost electrolytes. This review will focus on intentional perspiration for the treatment of patients with end-stage renal disease (ESRD). Studies have shown that perspiration, or sweat-based therapies, can provide some of the most important currently recognized therapeutic goals in treating ESRD. These goals include decreased interdialytic weight gain, reduced serum potassium levels, and benefits to cardiovascular status. Research has shed light on some of the mechanisms, both molecular and clinical, that may be involved in induced perspiration therapy in ESRD. SUMMARY: There is a long history of humans using perspiration for both recreation and therapy. Perspiration therapy for ESRD experienced a surge in the United States in the 1960s but does not have much modern momentum. With the continued growth of the ESRD population worldwide this could be considered an appropriate time to conduct more research into this promising therapy.

Microfluidic Chip-Based Wearable Colorimetric Sensor for Simple and Facile Detection of Sweat Glucose.

This study reports a microfluidic chip-based wearable colorimetric sensor for detecting sweat glucose. The device consisted of five microfluidic channels branching out from the center and connected to the detection microchambers. The microchannels could route the sweat excreted from the epidermis to the microchambers, and each of them was integrated with a check valve to avoid the risk of the backflow of the chemical reagents from the microchamber. The microchambers contained the pre-embedded glucose oxidase (GOD)-peroxidase-o-dianisidine reagents for sensing the glucose in sweat. It was found that the color change caused by the enzymatic oxidation of o-dianisidine could show a more sensitive response to the glucose than that of the conventional GOD-peroxidase-KI system. This sensor could perform five parallel detections at one time. The obtained linear range for sweat glucose was 0.1-0.5 mM with a limit of detection of 0.03 mM. The sensor was also used to detect the glucose in sweat samples from a group of subjects engaged in both fasting and postprandial trials. The results showed that our wearable colorimetric sensor can reveal the subtle differences existing in the sweat glucose concentration after the fasting and the oral glucose uptake.

A Wearable Paper-Based Sweat Sensor for Human Perspiration Monitoring.

The fabrication and performance of a wearable paper-based chemiresistor for monitoring perspiration dynamics (sweat rate and sweat loss) are detailed. A novel approach is introduced to measure the amount of aqueous solution in the order of microliters delivered to the sensor by monitoring a linear change in resistance along a conducting paper. The wearable sensor is based on a single-walled carbon nanotubes and surfactant (sodium dodecylbenzenesulfonate) nanocomposite integrated within cellulose fibers of a conventional filter paper. The analytical performance and the sensing mechanism are presented. Monitoring sweat loss in the human body while exercising is demonstrated using the integration of a wireless reader and a user-friendly interface. By addressing the barriers of cost, simplicity, and the truly in situ demanding measurements, this unique wearable sensor is expected to serve in the future in many different applications involving the on-body detection of biofluids, such as a monitoring tool of dehydration levels for athletes as well as a tool for enhancing the sport performance by providing an accurate recovery of the hydration status in daily exercises.

[Value of sweat conductivity testing in the diagnosis of cystic fibrosis in children].

Objective: To assess the diagnostic value of sweat conductivity testing in Chinese children with cystic fibrosis (CF). Methods: This is a retrospective study. Sweat conductivity tests were conducted in 45 CF children (CF group) and 200 non-CF children (non-CF group) diagnosed with other chronic pulmonary diseases at the No. 2 Department of Respiratory Medicine, Beijing Children's Hospital from May 2014 to June 2018. Pearson's chi-square test was used to assess the differences between CF and non-CF groups. A receiver operating characteristic curve was constructed to calculate the best cut-off value to diagnose or rule out CF. The pulmonary function parameters (forced expiratory volume in the first second, forced vital capacity,forced expiratory flows at 75% of exhaled vital capacity) of CF children over 6 years old were analyzed. The relationship between sweat conductivity and pulmonary function was compared between the two groups (80-120mmol/L vs.>120mmol/L). Results: The age of CF group was 9 (7,12) years old, 19 males (42%) and 26 females(58%); the age of non-CF group was 8 (5,11) years old, 106 males (53%) and 94 females(47%). The results of sweat conductivity test showed that sweat conductivity in CF group 108(99, 122) mmol/L was significantly higher than that in non-CF group 43(36, 52) mmol/L (χ(2)=207, P<0.01). A cut-off value of 80 mmol/L for CF diagnosis showed a sensitivity of 93.3% and a specificity of 98.5%. The receiver operating characteristic curve analysis suggested the best conductivity cut-off value for the diagnosis of CF was at 83.5 mmol/L,with a sensitivity of 93.3% and a specificity of 100%,and an area under the curve of 0.993 (95% confidence interval 0.985-1.000). The best conductivity cut-off value to rule out CF diagnosis was at 63.5 mmol/L,with a sensitivity of 97.8% and a specificity of 90.5%. There was no correlation between the level of sweat conductivity and the extent of pulmonary function decline. Conclusions: Sweat conductivity testing can be used for the screening of CF in Chinese children. A diagnosis of CF should be considered if the value is greater than 80 mmol/L.

Why does sweat lead to the development of itch in atopic dermatitis?

Sweating plays an important role in maintaining temperature homeostasis in humans. However, under certain circumstances, sweat can cause itching. For example, when excessive sweat accumulates on the skin surface for a long period, miliaria can develop and cause itching. Subjects with dermatoses, such as atopic dermatitis (AD), suffer from itch when exposed to heat or psychological stresses, which are also known perspiration stimuli. Recently, some mechanisms of sweat-induced itch have been revealed. For instance, attenuated sweating ability is observed in subjects with AD, causing heat retention, skin dryness, and high susceptibility to itch. Furthermore, the decreased tight junction of the sweat gland in AD leads to sweat leakage in the dermis, which could be designated as a "sweat endocrine response" and may be the cause of tingling itch during sweating. Additionally, metabolomic analysis of sweat from patients with AD revealed that glucose concentration in sweat increases according to disease severity. Sweat with elevated glucose concentration retards the recovery of the damaged skin barrier and may promote itching. This viewpoint essay outlines the relationship between sweat and itch based on recent evidence.

Sunscreen or simulated sweat minimizes the impact of acute ultraviolet radiation on cutaneous microvascular function in healthy humans.

NEW FINDINGS: What is the central question of this study? Are ultraviolet radiation (UVR)-induced increases in skin blood flow independent of skin erythema? Does broad-spectrum UVR exposure attenuate NO-mediated cutaneous vasodilatation, and does sunscreen or sweat modulate this response? What are the main findings and their importance? Erythema and vascular responses to UVR are temporally distinct, and sunscreen prevents both responses. Exposure to UVR attenuates NO-mediated vasodilatation in the cutaneous microvasculature; sunscreen or simulated sweat on the skin attenuates this response. Sun over-exposure may elicit deleterious effects on human skin that are separate from sunburn, and sunscreen or sweat on the skin may provide protection. ABSTRACT: Exposure to ultraviolet radiation (UVR) may result in cutaneous vascular dysfunction independent of erythema (skin reddening). Two studies were designed to differentiate changes in erythema from skin vasodilatation throughout the 8 h after acute broad-spectrum UVR exposure with (+SS) or without SPF-50 sunscreen (study 1) and to examine NO-mediated cutaneous vasodilatation after acute broad-spectrum UVR exposure with or without +SS or simulated sweat (+SW) on the skin (study 2). In both studies, laser-Doppler flowmetry was used to measure red cell flux, and cutaneous vascular conductance (CVC) was calculated (CVC = flux/mean arterial pressure). In study 1, in 14 healthy adults (24 ± 4 years old; seven men and seven women), the skin erythema index and CVC were measured over two forearm sites (UVR only and UVR+SS) before, immediately after and every 2 h for 8 h post-exposure (750 mJ cm-2 ). The erythema index began to increase immediately post-UVR (P < 0.05 at 4, 6 and 8 h), but CVC did not increase above baseline for the first 4-6 h (P ≤ 0.01 at 6 and 8 h); +SS prevented both responses. In study 2, in 13 healthy adults (24 ± 4 years old; six men and seven women), three intradermal microdialysis fibres were placed in the ventral skin of the forearm [randomly assigned to UVR (450 mJ cm-2 ), UVR+SS or UVR+SW], and one fibre (non-exposed control; CON) was placed in the contralateral forearm. After UVR, a standardized local heating (42°C) protocol quantified the percentage of NO-mediated vasodilatation (%NO). The UVR attenuated %NO compared with CON (P = 0.01). The diminished %NO was prevented by +SS (P < 0.01) and +SW (P < 0.01). Acute broad-spectrum UVR attenuates NO-dependent dilatation in the cutaneous microvasculature, independent of erythema. Sunscreen protects against both inflammatory and heating-induced endothelial dysfunction, and sweat might prevent UVR-induced reductions in NO-dependent dilatation.