According to Virgina Zarulli, an associate professor of demography at the University of Southern Denmark, the two main causes are biological.
Estrogen may be the answer. Women tend to produce more estrogen than men, and estrogen provides protection against a range of diseases, including cardiovascular diseases, according to a 2017 study in the journal Biology of Sex Differences.
While women produce more estrogen, men produce more testosterone, which, in high amounts, can cause cancers in both men and women. In women, it's linked to endometrial and breast cancer, and in men it's linked to prostate cancer.
The difference in chromosomes also plays a role. Where most men have an X and a Y chromosome, most women have two X chromosomes.
"If you think about that, the Y chromosome is an X chromosome with a missing leg. It's missing genetic material," Zarulli said. "Women have this double X chromosome — extra genetic material — which allows them to, for instance, have a backup plan if there is a bad mutation on one of the two X chromosomes. The other X can let them live anyway."
Social factors also play a large role. Men tend to smoke more cigarettes and are nearly twice as likely to binge drink alcohol, according to the CDC. Women are also 33% more likely to visit a doctor.
However, this wasn't always the case. According to Our World in Data, women didn't live longer than men in the 19th century.