Infrared thermography (IRT) is a non-invasive tool widely used to measure skin temperature (Tsk) in various health and sports applications. The ability of thermography to detect subtle changes in the body's surface temperature makes it an excellent tool for monitoring an individual's internal load.

The determination of normative skin temperature values has been a recurrent topic in scientific research. These values serve as a reference to identify deviations in temperature that may indicate abnormalities or the need for intervention, both in health and sports fields. Over the years, many studies have attempted to establish these normative values but have encountered significant limitations, such as small sample sizes and the use of manual methods to define regions of interest (ROI).

Below, we present a study introduced at the XVI Congress of the European Association of Thermology. The main objective was to collect data from a much larger sample and use an automatic method to analyze thermal images (utilizing Thermohuman software). This approach aimed to provide a more robust and statistically relevant dataset of normative skin temperature values in a young and healthy population, while also exploring gender differences.

Methods.

Thermal images of 3,626 healthy and physically active subjects were collected by the same observer. Among them 3,088 were male (Men) (Age: 25.21 ± 6.24 years) and 538 were female (Women) (Age: 24.72 ± 10.87 years). The data collection was performed in different locations in Europe, using the same camera (FLIR T530, 320x240 pixels resolution, <30 mK) and following TISEM consensus (Ambient Temperature: 22.40 ± 2.06ºC degrees, relative humidity between 30% and 50%). All thermal images were automatically analyzed using ThermoHuman software, which extracted average temperature and standard deviation from 94 Regions of Interest (ROI). T Student test was used to check significant differences among from Men and Women groups.

Results.

The average temperature of all ROIs was 31.68±1.56ºC. The warmest ROIs are located in the trunk and the coldest ones in distal ROIs and joints such as Knee or Ankle. In the case of the Men values, the average temperature was slightly higher than Women (31.76±1.45ºC in Men and 31.18±1.88ºC in Women). When comparing ROIs from both groups, most of them did show significant differences between both groups (p value<0.01). Only a few ROIs did not show significant differences, such as Abdomen, Wrist, Foot, Trapezius, Cervical Spine, Forearm and Gluteus (p value>0.05).

Discussion.

The general values presented in this study are similar to those reported by Chudecka and collaborators (2015). The primary reason for this similarity is likely the focus on young, physically active European subjects in both studies. Conversely, other publications have shown normative values that are more than 1ºC cooler (Zhang et al., 2023; Bouzas Marins et al., 2014; Niu et al., 2001). These variations can be attributed to several factors: firstly, differences in the ROIs analyzed (manual vs. automatic); secondly, differences in the age, fitness, and regional characteristics of the samples; and thirdly, differences in the thermal cameras used. Additionally, the results highlighted significant differences in most ROIs between men and women, confirming that men have significantly higher skin temperatures than women in almost all ROIs. These findings are consistent with previous studies (Zhang et al., 2023; Bouzas Marins et al., 2014; Chudecka et al., 2015) and may be related to differences in skeletal muscle mass (SMM) and subcutaneous fat mass (SFM).

Conclusion.

• The study, using a larger sample size, standardized protocols, and an automatic processing system, shows warmer skin temperature values in central ROIs and cooler temperatures in the extremities and joints.
• Despite variability in published normative skin temperature data, results similar to this study align in terms of region, fitness, and age.
• Men exhibit higher normative skin temperature values than women, likely due to greater skeletal muscle mass (SMM) and lower subcutaneous fat mass (SFM).
• Standardized protocols are recommended to improve data quality.
• Future research should explore regional, age, and gender-specific variations in skin temperature to enhance the application of infrared thermography (IRT) in various fields.

References.

• Bouzas Marins, J. C., Andrade Fernandes, A., Piñonosa Cano, S., Gomes Moreira, D., Souza da Silva, F., Amaral Costa, C. M., . . . Sillero-Quintana, M. (2014). Thermal body patterns for healthy Brazilian adults (male and female). Journal of Thermal Biology, 42(0), 1-8. doi:http://dx.doi.org/10.1016/j.jtherbio.2014.02.020
• Chudecka, M., & Lubkowska, A. (2015). Thermal maps of young women and men. Infrared Physics & Technology, 69(0), 81-87. doi:http://dx.doi.org/10.1016/j.infrared.2015.01.012
• Gomes Moreira, D., Costello, J. T., Brito, C. J., Adamczyk, J. G., Ammer, K., Bach, A. J. E., . . . Sillero-Quintana, M. (2017). Thermographic imaging in sports and exercise medicine: A Delphi study and consensus statement on the measurement of human skin temperature. Journal of Thermal Biology, 69, 155-162. doi:https://doi.org/10.1016/j.jtherbio.2017.07.006
• Niu, H. H., Lui, P. W., Hu, J. S., Ting, C. K., Yin, Y. C., Lo, Y. L., Liu, L., & Lee, T. Y. (2001). Thermal symmetry of skin temperature: normative data of normal subjects in Taiwan. Zhonghua yi xue za zhi = Chinese medical journal; Free China ed, 64(8), 459–468.
• Zhang, H. Y., Son, S., Yoo, B. R., & Youk, T.-M. (2023). Reference Standard for Digital Infrared Thermography of the Surface Temperature of the Lower Limbs. Bioengineering, 10(3). doi:10.3390/bioengineering10030283