Partly this is because, for a given bodyweight, women tend to have less muscle tissue to generate heat. But the hormone oestrogen also has a big impact because it has the side effect of thickening the blood slightly. This
reduces blood flow to the tiny capillaries supplying the extremities. A 1998 study at the University of Utah found that this can mean women have hands, feet and ears that are 3°C colder than a man’s.