Menstruation 101



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Thinx - Periodical - Menstruation 101

by Team Thinx | June 28, 2022

what is a period?

Here at Thinx—as you can imagine—we spend a lot of time talking about menstruation. As the first menstrual product innovation in almost a century, we designed reusable period underwear as a more eco-friendly way to transform your cycle — with styles that absorb up to 5 regular tampons’ (and 2.5 regular pads’) worth of period flow. But what *is* menstruation actually? For many of us who have a handle on basic period knowledge, the nitty-gritty details may not be super clear. That’s why we put together a quick explainer on what menstruation is, why it happens, and a breakdown of all the phases of your menstrual cycle.

what actually happens during menstruation?

While most of us received a rudimentary education about periods in grade school (which probably involved first kicking all the boys out of the room), it’s possible the specifics have become a bit fuzzy since then. Here’s the thing — on average, you’ll menstruate for 3,000 days in your lifetime. That’s a lot of time to be kind of hazy on the details! So, let’s take this opportunity to go back to the basics: What’s actually going on down there all month?

In a nutshell, if you menstruate, your body is always preparing for one of its eggs to be fertilized. The lining of your uterus will thicken around one of your eggs, creating a cozy home in preparation for a fertilized egg. If you don’t become pregnant, your body sheds the lining and releases the unfertilized egg. Then, the cycle starts all over again! Let’s break that down.


Day 1 of your period is also day 1 of your whole menstrual cycle. This is when your body gets rid of unneeded stuff: the uterine lining, the unfertilized egg, and mucus. And of course, blood flows out your uterus through your vagina and into your pad, cup, or tampon — or into your Thinx underwear, if you’re free bleeding! As you’re probably aware, menstruation tends to last 3 to 7 days and is accompanied by all sorts of fun things like cramping, mood swings, fatigue, and more.

follicular phase

Did you know we’re born with all the eggs we’ll ever have? We usually start with 1 to 2 million follicles (immature eggs), but by the time puberty comes and menstruation begins, the number has dropped to around 400,000. These immature eggs are stored in our ovaries, each inside its own microscopic, fluid-filled follicle. The follicular phase begins when 1 of about 20 competing follicles matures into an egg and ends with ovulation of 1 egg. The first day of your period coincides with your follicular phase, so you’re technically double-booked with menstruation for the first week.

Let’s talk hormones: In our brains, we have a gland called the hypothalamus, which is responsible for things like thirst, hunger, sleep, sex drive, and hormones. At the beginning of your cycle, the hypothalamus kicks things into gear by telling its buddy, your pituitary gland, to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). That’s when your follicle matures and starts preparing for ovulation, the next phase of menstruation. These multitasking follicles then release another hormone, estrogen, which causes the lining of your uterus to thicken in preparation for the fertilization of your egg.


Once your estrogen levels hit their highest point, your hypothalamus gets another message: Release a burst of LH. This surge causes one follicle to burst open and release an egg, which then travels into your fallopian tube. Ovulation typically lasts 1 day, usually around the 14-day mark of your cycle. Tracking when your period starts and ends can give you a better sense of when you ovulate. This is especially useful if you’re trying to get pregnant, or if you’re not using hormonal birth control and trying to avoid having sex when you’re fertile.

If you’re using hormonal birth control like the pill, you usually won’t ovulate because the constant level of synthetic hormones prevents the peak that kicks off ovulation. The bleeding you may experience every month when you take a pill break is actually not a period at all; it’s withdrawal bleeding that’s caused by your body taking a break from those hormones.

luteal phase

The luteal phase is when premenstrual syndrome (PMS) kicks in, with mood swings, bloating, fatigue, cravings — you know the drill. The follicle that popped that egg out then transforms into the corpus luteum. The corpus luteum releases progesterone that stabilizes your thickened uterine wall in anticipation of you becoming pregnant. Here’s where the road forks: If your egg was fertilized, your body will need its uterine lining to remain thick, so the embryo will begin to produce human chorionic gonadotropin (hCG), the hormone that shows up on a positive pregnancy test. But if your body is sure there’s no potential fetus, your estrogen and progesterone levels will decrease, and your uterine lining will begin to disintegrate, which will lead to the beginning of your period.

Now we’re back to square one, day 1 of your period, and you get to start the cycle all over again. (Yay!/?) The good news is that the more familiar you get with what’s going on with your body, the better you can prepare for each phase.

navigating PMS

Premenstrual syndrome, or PMS, is a term as colloquial as it is medical. It’s not at all surprising that PMS has been used by the patriarchy to trivialize female behaviors, actions, and motivations. PMS is a variety of physical and behavioral changes, such as irritability, bloating, and fatigue, that happen during the latter half of the menstrual cycle, and it is totally normal. More than 90 percent of people with periods experience one or more physical or mental symptoms in the days leading up to it because of the cyclical rise and fall of the hormones that drive ovulation, progesterone being the main culprit. Progesterone is also responsible for most of the crappy symptoms of pregnancy: bloating, gastric reflux, and mood changes. This hormone is incredibly necessary but can leave you feeling pretty crummy when the levels are high.

what is PMDD?

Things start to get complicated when this normal occurrence begins interfering with your life. According to the American College of Obstetricians and Gynecologists (ACOG), the true significance of PMS emerges when symptoms like depression, pelvic pain, and anger lead to economic and/or social dysfunction. Clinically significant symptoms that interfere with daily activities affect about 8 percent of people with periods. Premenstrual dysphoric disorder (PMDD) is a more severe version of PMS that affects only about 2 percent of people with periods. In PMDD, the effects of these hormonal shifts can be so severe that people become nonfunctional or suicidal, even during the latter half of their menstrual cycles. For people who are notably affected by these changes, there are many steps they can take to improve their overall quality of life. 

easing the symptoms

If you plot menstrual hormones (LH, FSH, estrogen, and progesterone) on a graph, it looks like an elaborate roller coaster ride, climbing and falling throughout the month. The easiest and most common treatment for PMS is hormonal birth control, because it essentially levels out the natural hormonal roller coaster. By blunting the effects of the highs and lows, and keeping hormones in a steadier state, the PMS symptoms also improve. The treatment for PMDD is typically hormones plus an antidepressant/anxiolytic medication, because hormonal birth control alone typically isn’t enough.

What about natural remedies for PMS? Certainly, people have been managing PMS since before modern medicine. The things that research has shown to work reliably are exercise and relaxation techniques (although typically in concert with medication). One study found women who exercised regularly had lower rates of impaired concentration and pain on a standardized menstrual distress questionnaire. However, supplements, including vitamin B6, vitamin E, chaste tree, calcium, and magnesium, don’t seem to be any more effective than placebos in managing symptoms.

Acupuncture is another therapy that gets a lot of media attention for a variety of health conditions, including PMS. However, it’s not a one-size-fits-all approach, but rather a crafted, holistic treatment plan for each individual. It’s difficult to rigorously study and academically vouch for a therapy we can’t standardize across participants. For medical professionals to officially recommend a therapy, we have to be able to prove it’s both effective and safe. This means there’s inevitably going to be a lot of gray area when treating conditions like PMS, because we just don’t have all the research we need yet. However, when you consider the true desperation some people feel while experiencing PMS—and especially PMDD—the best management approach is one that considers all options, so long as they’re safe and effective for the person.

Managing PMS in real life is as much a roller coaster as the menstrual cycle itself. Staying well informed and keeping an ongoing, open dialogue with your healthcare provider about your options is the first step toward reclaiming control of your body.

This article originally appeared in The Vagina Book: An Owner’s Manual For Taking Care of Your Down There, written by Thinx and Dr. Jenn Conti.

by Team Thinx

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