Concerns about whether human menstrual fluid attracts wildlife, particularly in wilderness settings, are common and often stem from long-standing folklore. This safety question frequently arises for individuals planning outdoor activities in areas inhabited by large mammals. Separating fact from speculation requires examining the fluid’s biological composition and the sensory abilities of the animals in question. While animals possess a highly developed sense of smell capable of detecting complex organic compounds, the scientific evidence regarding aggressive attraction to human menstrual odors is far less dramatic than the myth suggests.
Composition and Animal Olfaction
Menstrual fluid is not solely composed of venous blood, differentiating its scent profile from that of a fresh wound. The fluid is a complex biological mixture of blood, shed endometrial tissue, mucus, proteins, and cells. Approximately 75% of the fluid is arterial blood, with the remainder being venous blood mixed with these other biological components.
The presence of shed tissue and the process of fibrinolysis, which prevents the fluid from clotting, create a unique chemical signature. This composition includes various volatile fatty acids and other organic compounds that contribute to the distinct odor. Large mammals, such as bears, possess an incredibly sophisticated olfactory system, with a nasal turbinate area significantly larger than that of humans.
This highly tuned sensory apparatus allows them to detect minute concentrations of scents, especially those associated with food sources. The concern over menstrual odor arises because a bear’s sense of smell is designed to investigate any unusual or complex organic scent in its territory. However, the ability to detect a scent does not automatically equate to being aggressively attracted to it as a prey source.
Evidence of Attraction
The most significant studies concerning menstrual blood and animal attraction have focused on bears, particularly in North American national parks. A persistent myth linking menstruating women to bear attacks largely traces back to a single 1967 incident in Glacier National Park, which led to speculation but lacked scientific confirmation. Subsequent scientific review of hundreds of grizzly bear attacks found no statistical correlation between the attacks and the menstrual cycle of the victims.
Field experiments involving black bears yielded similar results, showing little to no interest in menstrual odors. A 1991 study exposed 26 free-ranging black bears to used tampons and directly to four menstruating women; the bears essentially ignored the scents. The consensus among wildlife biologists is that food remains the overwhelmingly dominant attractant for both black and grizzly bears.
An exception was noted in a 1983 study involving captive polar bears, which responded strongly to used tampons, similar to their reaction to seal scents. This specific attraction is believed to be linked to the polar bear’s hyper-carnivorous diet and the unique environmental conditions of the Arctic, where low food availability may prompt investigation of unusual organic material.
The idea that menstrual blood attracts sharks is also unfounded. The volume of blood released into a large body of water is minimal, and the fluid’s composition is not the scent profile sharks associate with their natural prey. Sharks are much more likely to be attracted to the chemical signals of distressed fish or the erratic movements of a swimmer, not the trace amounts of human menstrual fluid.
Safe Management of Menstrual Waste
Regardless of the low-risk scientific findings, responsible wilderness practice dictates managing all scented human waste to minimize wildlife habituation and maintain a clean environment. Disposable products, such as tampons and pads, must always be packed out, as they are not biodegradable and can be dug up by curious animals. Used disposable products should be sealed in an opaque, odor-proof container, such as a zip-top bag double-wrapped in duct tape, to contain scent.
Adding a few tea bags, coffee grounds, or crumbled aspirin to the waste bag can help neutralize or mask residual odors. This sealed waste should then be stored with all other smellable items, including food and toiletries, inside a bear canister or hung from a tree using a bear-resistant technique.
Reusable products, like menstrual cups, offer a simpler alternative for waste disposal, as the fluid itself can be treated like other human waste. Contents of the cup should be emptied into a small hole, known as a cathole, dug six to eight inches deep, positioned at least 200 feet away from water sources, trails, or campsites. The cup can then be rinsed with clean water or wiped with toilet paper before reinsertion. For thorough cleaning, the cup should be sterilized by boiling it in water once back at a safe campsite or home.