The Surprising Way the Sweltering Summer Heat Affects Your Mood

You’re not a nice person when it’s hot outside. But don’t be so hard on yourself: A new study says it happens to everyone.

The next time a friend calls you and asks for a favor, how willing you are to lend a hand may have a lot to do with one unexpected factor: the heat. Yup, according to a new study in the European Journal of Social Psychology, uncomfortably hot environments make us less likely to help others in need.

Past research has demonstrated—and we can certainly all agree—that a really hot day can induce feelings of grumpiness and even hostility toward everyone around us. But this is the first study to show a link between ambient temperature and “prosocial” behaviors, which are essentially those selfless deeds that benefit other people, organizations, or society as a whole, but not explicitly ourselves.

To study this connection, researchers from Lehigh University and Northwestern University performed three experiments. In the first, they found that retail store employees were 50 percent less likely to engage in prosocial behaviors—like volunteering to help customers, listening actively, and making suggestions—when they were working in an uncomfortably hot store compared to normal conditions.

In the second experiment, even just thinking about hot temperatures was enough to influence helping behaviors. Half of the participants taking a paid online survey were asked to recall situations in which they were uncomfortably hot, and then all of the participants were asked to take another survey for no additional compensation. Only 34 percent of the people who imagined feeling hot were willing to complete the free survey, versus 76 percent of a control group.

Finally, the researchers asked college students seated in either a 69-degree room or an 80-degree room to fill out a survey that would benefit a local non-profit organization. Only 64 percent of the students in the hot room agreed to answer at least one question, compared to 95 percent in the cool room. And those in the hot room who did participate answered only about one-sixth of the questions those in the cool room did.

The researchers were able to show that hot and muggy environments increased fatigue and reduced positive mood, which directly led to less helping behavior. Understanding this connection may help people better anticipate—and possibly prevent—these types of harmful or undesirable behaviors, they say. “Even though one cannot control or change the weather itself, it is feasible to control one’s ambient environment,” they wrote in their paper.

Lead author Liuba Belkin, Ph.D., associate professor of management at Lehigh University, says the study can offer important advice to workplace supervisors and group leaders. “If managers would like to encourage prosocial behavior in their organizations under adverse environment, they should try to minimize job-related stress and create comfortable environments for employees,” she says. Expressing empathy and trying to think about situations from their employees’ point of view may also help, she adds.

As an organizational psychologist, Belkin doesn’t have specific advice for individuals who may find themselves in these uncomfortable situations. But now that we know about this strange side effect of hot weather, it gives us even more incentive to stay cool all summer long. Plus, we’ll be sure to make an extra effort to be helpful to those around us—no matter what the temperature.