4 Very Cool Scientific Facts about Your Menstrual Cycle

4 Very Cool Scientific Facts about Your Menstrual Cycle

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A lot of people think it’s weird to talk about periods, but not us. Menstrual cycles are part of our biology, just like the nervous system or the billions of cells that make up our bodies. The more you know about how they work, the less weird or gross they seem.

Ready to nerd out with us? Here are four cool things about your cycle – and the science behind them.

1. Period blood isn’t the same as blood from another part of your body

You can tell just by looking – if you cut your finger, the blood appears different from what shows up in your underwear. That’s because what comes out during a period is actually the lining of the uterus, a mixture of blood and tissue. Your body builds up the lining of your uterus each cycle in preparation for potential pregnancy. But if an egg isn’t fertilized by a sperm, the thickened lining of the uterus is shed through the vagina. This is your period.

2. Humans menstruate in a unique way from other species

Humans are among a select few animals that release their uterine lining in a visible menstrual period. Why is this? Several theories have been proposed, but recent research indicates it’s because humans have a distinctively thick uterine lining. If an egg meets a sperm and fertilization occurs, the developing pregnancy sets down “deep roots” in the uterine lining. This built up blood and and tissue lining supports the pregnancy’s attachment and development while also protecting the mother. If fertilization doesn’t happen, the amount of lining is too substantial to be completely resorbed (resorption is common in many other animal species who build up their uterine lining), and so we shed it through our period.

3. Early menstrual cycles can be anywhere from 21-45 days – and that’s totally normal

During the first year of menstruation, your menstrual cycle is likely to be irregular in length and flow: short then long, heavy than light. Why? Some of this irregularity is due to what’s called an anovulatory cycle. An anovulatory cycle means you didn’t ovulate – no egg was released. These are thought to occur in early menstruators because the hormonal system/circuitry that regulates your cycle is still maturing.

Bleeding like a period still occurs during anovulatory cycles, but it’s usually different from the bleeding you experience during a regular (ovulatory) cycle. Anovulatory cycles are also usually longer than a regular cycle. So while a 21-45 day long cycle is considered normal for early menstruators, occasionally having one that’s shorter than 20 or longer than 45 days is possible. (However, if you regularly have a cycle that’s shorter than 20 or longer than 45 days, it’s time to check in with your healthcare provider).

4. Everyone has their own cycle that’s unique from everyone else’s

Shorter and more regular cycles come with age. By the third year of having a period, 60-80% of cycles are 21-34 days long (that’s the average cycle length for adults). By the sixth year of having a period, most people have established a personal norm for their cycle.

That’s great, but how do you know what’s normal for you? By tracking, of course! Here’s what we and many others have found helpful to track in Clue:

  • Cycle length: day one of your period is day one of your cycle.
  • Period length: record the number of days you bleed
  • Flow: Record amount (as number of menstrual product changes) and color/consistency of menstrual flow.
  • Record PMS-like and pain symptoms throughout cycle.

Now you know a bit more about the geeky cycle science of the human body. We hope you find periods and cycles as nerdily awesome as we do.

This article was written by Clue, a menstrual cycle tracking app that’s full of information about periods, ovulation, and PMS focused on facts and figures instead of myths and misconceptions.