Time Course of Cortisol Loss in Hair Segments Under Immersion in Hot Water

The study investigated the effects of environmental factors, such as ultraviolet (UV) irradiation and immersion in hot water, on hair cortisol content, which is a potential biomarker for chronic stress. It was found that these factors significantly reduced hair cortisol levels, with a two-stage loss process observed during long-term immersion in hot water. The study involved 30 participants and confirmed that hair cortisol content varied by location on the head, with the posterior vertex showing the highest and most consistent levels. The findings suggested that hair cortisol from the posterior vertex could more accurately reflect central hypothalamo–pituitary–adrenal activity.