Cortisol, our primary stress hormone, may go up and down a lot over holiday breaks, Robin Edelstein, an associate professor of psychology who studies hormones and relationships at the University of Michigan, told Insider. ¶¶”For some people, going home could be this very comforting experience, which could lower stress, decrease cortisol,” she said. But that is not always the case. For example, imagine you’re about to miss your flight, and you’re running for the gate. ¶¶”Cortisol would go up really quickly,” Edelstein said.