A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Are bears more likely to attack menstruating women?

June 12, 1992

Dear Cecil:

One of the highlights of my year is an all-girl backpacking trip with a group of friends. I mentioned this at a party recently, only to have some (male) geek give me dire warnings about women camping while on their periods. He claimed bears are irresistibly attracted to the scent.

I checked with one of my more experienced camping buddies, who said she'd heard the same story but attributed it to another fiendish male plot to keep us in the kitchen. Since this year's trip is planned for Yosemite, which is known for its bear population, I thought I'd better get the straight dope. Should we be concerned? Or just more careful about whom we converse with at parties?

Cecil replies:

Oh, I dunno. Even dweebs have their entertainment value. Dubious as this business about bears being attracted to menstruating women may sound, however, it can't be entirely dismissed. Two menstruating women were killed by grizzly bears in Glacier National Park in 1967, and the authorities have been warning women to stay out of bear territory during their periods ever since. There's been a fair amount of research, some of it conducted by women, suggesting that omnivores and carnivores (e.g., bears) are inspired to attack by the smell of human blood, while herbivores (e.g., deer) are repelled by it.

The key here is blood, not necessarily menstrual blood. Research shows that deer are repelled by male blood, too. It's just that over time many animal breeds have learned humans mean trouble, some researchers believe, and women have the characteristic scent of human blood on them more often than men do.

Some think the attraction/repulsion of animals by human blood is one of the main reasons behind the menstrual taboos found in many primitive societies--a menstruating woman could play havoc with the hunt on which the tribe depended, and so was best kept out of sight during her period. For the same reason women often were not allowed on hunting trips.

This tidy theory has some flaws in it, though. Research has shown that deer, at least, aren't repelled by the equally pungent and far more abundant scent of human urine. What's more, while grizzly bears have been known to attack menstruating women, there have been no such attacks by black bears, which are much more common. Extensive research with black bears published in 1991 (the bears were given an opportunity to sniff bloody tampons, menstruating women played with wild but human-habituated bears, etc.) showed that black bears had virtually no reaction to menstrual blood.

The question is far from settled. Experiments in 1983 showed that polar bears were attracted to menstrual blood. And that 1967 attack does give one pause. I wouldn't cancel my camping trip if I were you, but if I were headed into grizzly country I might give some thought to timing.

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