The science of menstruation in 10 minutes | Dr. Jen Gunter

• Humans don't have pheromones—it's never been proven. So there's no such thing as 'cycle syncing.' Another myth that I hear is the menstrual cycle is a way to release toxins from the body. Well, if we needed the menstrual cycle to get rid of toxins, then I have bad news for women in menopause and all of men, right. Humans don't actually have toxins, and the menstrual cycle doesn't remove things from our body in the same way that the liver and the kidneys do. It's a myth that just needs to die.

Historically, education about the menstrual cycle has been dismal. It's all framed in context of pregnancy and preventing pregnancy, as opposed to about the menstrual cycle and what it means for a person's body. If we can't talk about it, if we can't share knowledge about it, then the implication is that it doesn't matter. But we know that the menstrual cycle has significant impact on the half of the population that has it.

We want people to know how much blood is too much, how much pain is a concern, has your period started too late— all these things are important to know about, so you can advocate for yourself. If you have a menstrual cycle, if you love someone who has a menstrual cycle, and I know that you came from someone who had a menstrual cycle, you should want everybody to be able to access the same level of care.

Hi, my name's Dr. Jen Gunter. I'm a San Francisco Bay Area OBGYN and author and health communicator, and my latest book is, "Blood: The Science, Medicine, and Mythology of Menstruation." Relatively few mammals menstruate. So there's humans and some great apes. There are some bats. There is the spiny mouse and the elephant shrew. So it's kind of like this motley crew of species.

Every other mammal has an estrous cycle, which is a little different. The word "menstruation" comes from both a Latin and a Greek root, and it's for the word for "monthlies" or a "monthly occurrence." And so it reflects the idea that the menstrual period was expected to come about once a month like the Moon. Many people have historically believed that the menstrual cycle was every 28 days. There really is no scientific proof for that. It might be an average at some ages, but there's actually quite a bit of variation even cycle to cycle, so it could be very normal for you to have a 26-day cycle for one cycle, and then the next one it be 32 days.

A menstrual cycle means that the lining of the uterus has undergone a change called 'decidualization.' So the beginning of the cycle starts actually with the first day of bleeding. And for humans, that happens after ovulation occurs and is due to the release of progesterone. Decidualization is a real physical change in the tissue, and if you want to think about the decidua as kind of like a catcher's mitt in the uterus, it's all prepared and ready for an embryo. If there's no decidualization, implantation can't occur.

When you have an estrous cycle, the trigger comes from the embryo itself. So you don't have to have that catcher's mitt waiting there. One analogy that I often use is with humans it's like the restaurant's making a dish—whether or not you show up, it's gonna be made. But with estrous, it's only making the dish if it's been ordered. Humans have an incredibly invasive placenta that has to be handled or it could grow through the uterus and cause problems. So humans have evolved to deal with that.

In addition, the decidua actually senses embryo fitness and is part of regulating which pregnancies actually take, and which are incredibly early miscarriages. So, what happens when you don't get pregnant in a cycle is that you have this big, thick tissue that's got nowhere to go. It can't be reabsorbed by the body, and so menstruation involves chemical changes that cleave the decidua from the uterus, opening up blood vessels that then push that fluid out with the decidua, the tissue, and then the cycle can start anew.

There is this romanticization about nature that nature has everything perfect, and I think that nature's motto is probably best summed up as "Just good enough," right? You're half-dressed and slapped you on the back, and push you out the door. You're just good enough, "Go on, go on out into the world," because evolution doesn't care about an individual person's suffering. It cares: is this design going to work enough to perpetuate the species?

I often think that this is another reason for everybody to know about menstruation, because the pain and the problems associated with perpetuating the species have been uniquely born by half the population. There are a constellation of negative symptoms that can be associated with the menstrual cycle. Premenstrual syndrome is a constellation of symptoms that happen only in the luteal phase, so after ovulation, and those can include breast tenderness, moodiness, feeling of hopelessness or 'anhedonia,' and food cravings, which are really very common.

People can also get menstrual diarrhea, which again, happens at the same time, either right before or during the menstrual cycle. There's also pain that can happen with ovulation, which is 'mittelschmerz,' which we believe is actually more related to a muscle spasm that's triggered by the chemicals that are released with ovulation. Then there are menstrual cramps, and those can vary in significance from being mild to being incredibly severe.

To put it in perspective, the amount of pressure generated when someone has, you know, menstrual cramps, it can be the same as the pressure generated in labor when you're pushing—and I'll add that some people have equated the pain in labor as equivalent to cutting a finger off without an anesthetic. We think that menstrual cramps exist as part of the mechanism to stop bleeding. And among those chemicals that are produced are substances called 'prostaglandins.' Prostaglandins trigger pain. They also trigger the uterus to contract.

So you have all this chemical soup to stop the bleeding, you have things that cause vasospasms that cause those blood vessels to contract down. The uterus cramps down the same way that you put pressure on a wound to stop bleeding. Cramping itself is painful. The reduction in blood flow is painful, and some of the chemicals that are reduced can also affect pain thresholds.

One of the most common treatments for menstrual pain are taking non-steroidal anti-inflammatory drugs that we also call 'NSAIDS,' and what these drugs do are they block prostaglandins. However, when they don't help, that can be a sign there's something else causing your pain like endometriosis. But also, for some people, they just don't work well, and we don't really understand why that is, but that is an evidence-based approach to treating menstrual pain: taking medications that block prostaglandins.

• Prostaglandins seem like a troublemaker.
• Yeah, prostaglandins my old foe. But prostaglandins are important in our body in all different kinds of ways. It's not just a menstrual cycle-related chemical, but we do think as far as menstrual pain and menstrual diarrhea that they are the big troublemakers.

People use apps for their menstrual cycle in a couple of different ways. They may use them just as a tracker to see kind of what's going on, and they may also use them as part of a fertility awareness method. There's also a lot of talk on social media about athletes using their menstrual cycle to optimize performance, and none of that is really grounded in good science. There is no robust data there at all to support that.

Now, it is true that if you're trying to optimize your physical fitness, there may be times of the month where, for example, if your breasts hurt, you might not want to do upper body working, right? So you're listening to your body. Those are kind of intuitive. You don't need an app to tell you that.

One of the issues especially with menstrual tracking apps is many of them can be quite inaccurate. And there was a study where they looked at women who had tracked their cycles, and what happened was, when their period didn't come when the app predicted, the women blamed their bodies as opposed to blaming the app for being incorrect with the prediction, meaning:

Also, there is a dark side of apps, whether you're using them to just track your cycle or if you're using them as part of a fertility awareness method in that your data may not be secure. And there is definitely a concern for people who live in areas where not only is abortion illegal but people who have miscarriages are prosecuted as having abortions, that this data could be abused. I don't think it's a stretch that in some places this kind of data could lead to all kinds of problems down the road. So people just need to be very mindful about where we're going.

Ignorance about the menstrual cycle is clearly very common, even amongst medical providers. Weaponizing this ignorance is becoming law, and these are really troubling times. This is when people need to actually know the facts so they can speak up, because we are definitely seeing a shift towards viewing women solely as breeders—and that your life has less value than your role as basically carrying a pregnancy. I don't think we can sound enough alarms about that.

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