What Animals Can Smell Menstrual Blood? (Myths And Truths)

Have you ever heard that animals can smell menstrual blood and react to it aggressively?

Menstruation is a natural process in all women, but many live in fear of walking freely and without a worry in a forest or swimming at the beach, for fear that menstrual blood will attract an animal.

When asked this question, most people probably think of a shark first, but we are talking about an iguana. Because male iguanas react extremely violently to the pheromone released by females during their period.

It is true that many of the animals that are top predators can use the smell of their victims’ blood to track them, but in that sense, there is a lot of misinformation and myths related to menstrual blood in humans.

It should be taken into account that the reaction that triggers attraction in predatory animals to blood is their instinct to hunt wounded or weakened animals which are common prey for predators, menstrual blood is not a product of wounds and therefore its composition is different from body blood, and humans are nature’s top predators and are not common prey.

Which animals can smell menstrual blood?

The animals that are able to perceive the smell of menstrual blood are those that have a super-developed sense of smell, these animals possess Jacobson’s organ, also known as the vomeronasal organ.

Jacobson’s organ is present in dogs, cats, snakes, bears, mice, and other vertebrate animals, these animals may be able to smell menstrual blood because of their great sense of smell.

Although the fact that an animal has the ability to smell menstrual blood does not mean that it labels the menstruating person as potential prey, animals use their sense of smell simply to gather information from the environment.

And while it is true that animals that are predators use their sense of smell to track their prey, their instinct is sufficiently developed to be able to distinguish regular prey from what would be the menstrual blood of a human being.

Animals are able to distinguish prey, challenge, or threat through their sense of smell, their sense of smell and instinct is too well developed to mistake a menstruating human being.

Why are some animals attracted to blood?

A study by the Karolinkska Institute in Sweden published in Scientific Reports documented how predators and prey react to a very dilute and a seemingly imperceptible molecule called trans-4,5-epoxy-2 (E)-decenal – or, in short, E2D.

The molecule is liberated when lipids in the blood are broken down after contact with air. The researchers succeeded in separating the E2D from the blood and diluting it to a ratio of 1 ppt (one part per trillion). This corresponds to a single drop of the molecule in a pool the size of a

Menstrual blood is composed of water, dead endometrial cells, lipids, proteins, and hormones such as progesterone. It also contains a number of organic contaminants.

Are bears attracted to menstrual blood?

Many women in certain countries go out into the forest with the fear that when they are menstruating they are likely to be attacked by a wild bear, as there is a popular belief that bears like the smell of menstrual blood.

The conviction that bears attack menstruating women arose from an infamous incident in Glacier National Park in Montana in 1967 where two women were killed when attacked by grizzly bears.

A 1993 study published in The Journal of Wildlife Management by the U.S. Forest Service debunked the myth that bears attack when they smell the menstruation.

In that study, 5 grizzly bears were tested by having them sniff both foods in organic garbage and menstrual blood. The test results were conclusive, there was no interest or reaction to menstrual blood on the part of the bears.

Even more risky tests were carried out, where a group of women was put to live together for several months next to the bears, who were in charge of feeding them even when they were on their period. Finally, there were no violent episodes on the part of the grizzlies.

Can wolves and coyotes smell menstrual blood?

Both wolves and coyotes have the ability to smell menstrual blood, but they are unlikely to be attracted to menstrual blood because its composition is different from body blood, and these canids do not recognize humans as potential prey.

It should be noted that menstrual blood is not the same blood that runs through our veins, it has a different composition, therefore the odor is not the same.

And while both wolves and coyotes are predators that generally rely on their sense of smell and are attracted to blood, different studies and samples have determined that it is a specific molecule that causes this reaction in large canids.

As mentioned at the beginning of the topic, these animals have a great instinct for survival and hunting, this instinct makes them capable of detecting and recognizing humans, the large canids usually do not recognize humans as prey.

Can Sharks Smell menstrual blood?

First of all, the amount of blood you lose during your period is very small. On average, you only lose about one espresso cup of period fluid per period.

And this period fluid contains not only blood but also cervical mucus, vaginal secretions, and uterine lining. Accordingly, the amount of blood in the liquid is really not that big that it drives a shark crazy.

In addition, the liquid first has to pass your tampon or cup, which is even less likely due to the negative pressure in the water. This small amount of blood is then also diluted with the expanse of the ocean.

You are not reassured yet because you have heard that sharks can smell a drop of blood several kilometers away and that it makes them totally wild? First of all, this is not entirely true, because sharks can “only” smell prey odors at a concentration of one in a million over a distance of about 400 meters.

But that doesn’t mean that the sharks react bloodthirstily to every drop of blood. Otherwise, they would be completely overstimulated. In fact, not all sharks are attracted to blood.

And just because the sharks smell human blood (or rather the amino acids in it) doesn’t mean that they find it tasty, because humans are not exactly a delicacy in the shark world and period blood is also not a prey smell.

It is a myth that sharks can smell blood from miles away and are attracted to it, especially very dilute blood, a shark would probably not even be able to trace a drop of blood from a kilometer away and would surely not be able to find the source of the blood with that information alone.

So the answer to the question of whether sharks can smell the period must be: most likely yes, but they don’t care.

Iguanas can smell and react to menstrual blood

There are some known cases in America of menstruating females being attacked by iguanas. Veterinarians suspect that female iguanas smell similarly during courtship and that this odor irritates the animals in humans.

The iguana’s behavior is not due to an attraction to the smell of blood, since the iguana is not really a predator attracted to blood.

There is a theory that the smell of menstrual blood resembles that of a female iguana during courtship and that is why male iguanas may act aggressively in anticipation of a menstruating female.