The aim of this study was to analyze the basic responses of the endocrine system in young healthy men with moderate and high levels of PA, who were exposed to heat during four 12-min sessions in a Finnish sauna. There is a general scarcity of published studies investigating the impact of thermal stress on hormonal changes in men with different physical activity (PA) levels who are regular sauna users. Sauna sessions can trigger significant increases in growth hormone levels, with some studies showing up to a 16-fold boost. What's the difference between traditional and infrared saunas for hormonal health? Keep reading to learn if saunas can boost testosterone levels and how to use them to do so. If sauna use reliably lowers your baseline cortisol, it removes one of the primary suppressors of testosterone production. The concern is primarily relevant to extremely hot traditional saunas (100°C+) used for extended periods — well beyond typical infrared sauna sessions at 55-70°C. If sauna use improves body composition through GH stimulation and recovery enhancement, it supports better testosterone levels as a downstream effect. These systemic benefits help explain why repeated sauna exposure is often linked to improved body composition, better reproductive health, and more stable hormone levels. Many factors contribute to testosterone production, including age, genetics, diet, exercise, sleep quality, stress levels, and overall health. Near-infrared saunas utilize a different type of light therapy, which some studies suggest may offer additional benefits for hormone health. For men aiming to reduce body fat and maintain healthy testosterone levels, sauna therapy can accelerate metabolic activity and aid recovery after workouts. Elevated cortisol, the stress hormone, competes with testosterone production and can interfere with sperm health. The heat exposure in a sauna can stimulate the production of testosterone in the body, leading to potential improvements in overall levels. Cortisol affects metabolism by maintaining blood glucose levels at a sufficiently high level during physiological stress. COR is a catabolic hormone that is secreted by the adrenal cortex in response to physiological stress. Testosterone and COR levels can increase significantly even during low intensity exercise that is sufficiently prolonged (Brownlee et al., 2005; Väänänen et al., 2002). Testosterone plays a key role in triggering and maintaining sexual functions in males, and there is no scientific evidence to indicate that regular sauna bathing reduces male fertility (Kukkonen-Harjula & Kauppinen, 2006). In men, the increase in TES is particularly important for resistance-induced adaptations (Vingren et al., 2010), but a very high and rapid increase in serum TES and COR levels was reported immediately after high-intensity endurance exercise (Kreamer et al., 1995). Serum COR levels decreased significantly, whereas a significant increase in TES was not observed during repeated thermal stress and cold water immersion. Similarly to COR, TES increases linearly in response to exercise stress once a specific intensity threshold is reached, and its levels generally peak at the end of exercise (Wilkerson et al., 1980). In a study by Remes et al. (1979), the mean increase in hormone levels tended to be greater in the well-conditioned group than in the poorly conditioned group of army recruits. The relationships between different hormone concentrations before and after sauna and changes in these relationships in view of the participants’ PA levels (expressed in MET units) are presented in Table 2. After the sauna treatment, a very small decrease in COR concentrations was noted in men with very low baseline COR levels, and a minor increase or no change in COR concentrations were observed in four subjects.
