As finals approach, don't be surprised to find men and women reacting differently to seasonal stress, according to research by Laura Klein, assistant professor of biobehavioral health.

Women typically go through a "tend-and-befriend" response while under stress, as opposed to men, who experience a "fight-or-flight" response, Klein said. Tend-and-befriend behaviors include talking to friends, engaging in a social context and interacting with other people.

A fight-or-flight response triggers changes in the immune system, aggression, violence, anger and disrupted sleep.

Klein began her research on stress in the late 1990s in collaboration with Shelley Taylor, a researcher at UCLA. They conducted and analyzed studies involving both animals and humans that dealt with stress.

"In many of the studies, the results didn't match the research with men," Klein said. "Fight-or-flight triggers a biological cascade that women didn't always show."

She said she believes there is an evolutionary reason behind women's tendency to "tend-and-befriend." It would be disastrous for females who are pregnant, nursing or caring for children to fight or flee.

"Women have greater support networks," said Stacey Conway (graduate-biobehavioral health). "They have boyfriends, mothers and friends to help them deal with problems."

Psychologically speaking, women may just rely more on relationships.

"Women define themselves in terms of relationships," Conway said. "If something goes wrong, they are more likely to be affected than men."

Talking to friends often relieves stress, Hiewon Shin (graduate-English) said.

"It's nice to have someone to comfort me and to let me know that I'm not the only person who's stressed," Shin said.

The hormone oxytocin is a biological explanation for the tend-and-befriend response, Klein said. Oxytocin is produced by both sexes and it helps to relax, relieve depression, lower blood pressure and trigger affiliation.

Although present in both sexes, oxytocin has a greater effect on women. It is produced at a high level in nursing mothers and is enhanced by estrogen, a predominantly female hormone. Testosterone, a hormone associated with males, reduces the effect of oxytocin.

On the other hand, testosterone enhances the hormones that are released in a fight-or-flight reaction such as adrenaline, cortisol and epinephrine. These hormones increase blood pressure and aggression.

"When my husband is under stress, he doesn't want to talk to me," Shin said. "He wants to handle things by himself."

The different reactions of men and women to stress also causes some diseases to be more common in each sex, Klein said.

Since men more commonly have a flight-or-fight reaction, they have increased blood pressure, which leads to heart disease. After menopause when estrogen levels drop in women, heart disease rates rise.