The expression cold hands, warm heart may no longer ring true.

Yale University psychologists have found that people judge others to be more generous and caring after they hold a warm cup of coffee, compared to when they hold an iced coffee drink.

In a second study, the researchers found that subjects were more likely to give something to another person if they had just held something warm and more likely to take something for themselves if they held something cold.

"It appears that the effect of physical temperature is not just on how we see others, it affects our own behaviour as well," study co-author John A. Bargh, a professor of psychology at Yale, said in a statement. "Physical warmth can make us see others as warmer people, but also cause us to be warmer -- more generous and trusting -- as well."

The findings are published in the journal Science.

For their study, the researchers first asked undergraduate students to briefly hold either a warm or iced coffee.

They were then given a packet of information about a person and were asked to assess his or her personality traits.

The subjects were more likely to judge a person as warm if they had just held the warm coffee.

In the second study, the subjects held either heated or frozen therapeutic packs and were then offered a gift certificate to give to a friend or a gift that they would keep for themselves.

Those who held heated packs were more likely to accept the gift certificate for a friend, while those who held frozen packs were more likely to request the gift for themselves.

The researchers said their studies suggest that the words "warm" and "cold" to describe relationships or personality traits are not just metaphors.

They are descriptions for emotions such as trust, which humans develop during early experiences such as the bond between mother and child.

"When we ask whether someone is a warm person or cold person, they both have a temperature of 98.6 F," Bargh said. "These terms implicitly tap into the primitive experience of what it means to be warm and cold."