Despite campfire fears dating back to at least 1967, black bears and grizzly bears are not attracted to the odors of menstruation, according to a recent Yellowstone National Park report.

Polar bears may be interested in the smell of menstrual blood, the report found, but bears that roam in North America are not. Food is a much more important temptation for bears, according to the findings.

The idea that bears might preferentially attack menstruating women is not new. In 1967, a night of infamous grizzly bear attacks in Glacier National Park in Montana left two women dead. One woman was having her period, and the other was carrying tampons.

The attacks led to speculation that the women's menstrual odors might have "triggered" the attacks. The Park Service and other agencies even began warning women that bears might be attracted to the smell of menstrual blood, despite no scientific evidence to back up those warnings.

Since 1992, the Forest Services' Interagency Grizzly Bear Committee has tried to debunk this myth, but it has been difficult to dislodge. The new Yellowstone report, released in February, draws on a series of old studies to set the record straight. [7 Medical Myths Even Doctors Believe]

In one of these studies, conducted in 1991, researches exposed black bears, the most common kind of bear in the United States, to used tampons and to four menstruating women. They found no interest among any of the bears to the scents. Nor have researchers found any examples of black bears attacking menstruating women.

Nor are grizzly bears interested in women having their periods. A 1985 analysis of hundreds of grizzly bear attacks on humans found no evidence linking any of the attacks to menstruation — including the infamous "Night of the Grizzlies" attacks in Glacier. The two bears involved in those attacks were what biologists called "food conditioned," according to "Backcountry Bear Basics: The Definitive Guide to Avoiding Unpleasant Encounters" (Mountaineers Books, 2006) by Dave Smith. These bears were used to eating garbage and had begun to associate humans with food.

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The one exception to bears' disinterest in menstrual blood was the polar bear, the Yellowstone report finds. A 1983 study found that four captive polar bears exposed to a series of scents responded strongly only to seal smells and used tampons.

But as Smith points out in his book, the tests were limited to four bears and only 12 encounters with live, menstruating women. The bears were also much less interested in menstrual blood than any sort of food scent, eating used tampons half of the time they smelled them compared with 100 percent of the time for seafood and 92 percent of the time for seal oil. Even alcohol was more palatable to the polar bears than used tampons. They guzzled down beer 66 percent of the time. (They also ate unused tampons 13 percent of the time.)

At Yellowstone Park, the report concludes, there is no evidence of a link between bear attacks and menstruation. Nevertheless, the Park Service recommends using tampons instead of external pads and unscented menstrual products to keep potentially appealing odors down.

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