Wednesday, November 7, 2012

Bears Can Smell the Menstruation: Or Can They?

by Dr. Margaret Aranda

The question arises as to whether bears attack women who are on their periods, due to the attraction of the menstrual blood.  In 1983, Cushing presented his findings at the International Conference on Bear Research and Management, documenting the responses of polar bears to menstrual odors.  This spearheaded the future work in this area, which continues to this day.  Stay with me as we explore the fascinating issues surrounding this issue. 

The Grizzly Bear.

Yellowstone National Park (YNP) has been tabulating interactions between bears and humans in their district, which includes parks in Wyoming, Montana, and Idaho.  Data analyzed in 2012 by Kerry A. Gunther, bear biologist and expert at YNP’s Bear Management Program. He showed that the overall risk of human injury (for any reason) by a bear in YNP, men and women inclusive, is 1 in 2.1 million.  But the interest and fascination with this subject continues.

Kerry A. Gunther.

Perhaps the biggest outburst public scrutiny on bears attacking menstruating occurred after the night of August 13, 1967 in Glacier National Park.  The Park is located in northwestern Montana, along the Rocky Mountains.  In a situation that was later determined to be unrelated and coincidental, two women on their periods were killed by Grizzly bears on this night.  The National Park Service (NPS) subsequently put out a bulletin that menstruating women could be attacked by the Black Grizzly bear, perhaps spurring that speculation had turned into a scientific notion that the two were actually scientifically related.  The official statement was, “..women should stay out of bear country during their menstrual period.”  Years of belief ensued, wherein it was thought that camping or hiking women on their periods were attractants to killings by bears.

In his 1983 study on captive Polar Bears and the odor of menstrual blood, Cushing studied a series of different odors and their effect on bears.   Scents included seal scent, food, used tampons, and non-menstrual human blood.  There was a strong response to seal scent and used tampons.  Cushing also studied wild Polar Bears, who were attracted to and ate food and used tampons, perpetuating the observation that bears are attracted to menstrual blood.

In 1985, Herrero studied Grizzly bears and human attacks, including the two women attacked in 1967.  He concluded that there was no relationship.

In 1988, Byrd revisited the unsettled issue, trying to answer this question on his Thesis for his Master’s in Science.  He found that there was no evidence that the Black Grizzly bear preferred menstrual odors over other odors, and there was no scientific evidence that hundreds of bear attacks were related to women on their periods (Byrd 1988).

In 1991, Rogers et al studied how 26 wild Black Bears reacted to used tampons from 26 women.   In a novel design, he also studied 20 wild Black Bears’ response to 4 women’s menstrual blood at different times of their menstrual cycle.  The bears ignored the menstrual odors.

From 1980 through 2002, YNP had over 62,000,000 visitors spending over 15,400,000 nights at the main campgrounds and 956,000 nights in the backcountry.  No one kept track of statistics on the proportion of menstruating women.  There were 32 people injured by bears, coming to 1.2 injuries per year. Gunther and Hoekstra evaluated 1970 - 1994 statistics, citing that no bear injuries to humans were caused by menstruating women.  

Official word came out on August 9, 2012 from Kerry A. Gunther, who categorically stated that bears are not attracted to menstruating women. We can rest assured that if we keep the safety measures cited above, the risk would be so small as to be unproven.  So hat's away to camping, and be careful in the backwoods. 


Byrd, C.P.  Of bears and women: Investigating the hypothesis that menstruation attracts bears.  M.S. Thesis, Univ. Montana, Missoula.  129 pp, 1988.

Cushing, B. 1983. Responses of polar bears to human menstrual odors. International Conference on Bear Research and Management 5:270-274.

Gunther K.A. and H.L. Hoekstra.  Bear-inflicted human injuries in Yellowstone, 1970 – 1994, a cautionary and instructive guide to who gets hurt and why.   Yellowstone Science 4(1):2-9. 1997.

Herrero, S.M.  Bear attacks – their causes and avoidance.  Winchester Press, New Century Publishers, Inc.  Piscataway, New Jersey, 287 pp, 1985.

Nelson, Brian. Mother Nature Network.  Mentruating women do not attract bear attacks.  August 9, 2012.

_____.  Yellowstone National Park website.  National Park Service. Bears and Menstruating Women.

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