No matter how many times you may have read The Care and Keeping of You in middle school, periods (and how they work) are still pretty confusing. Maybe it’s because the awkward “maturation” video you had to watch in fifth grade didn’t explain anything beyond featuring a girl screaming about getting her “menses” in the library. Maybe it’s because sex education is woefully inadequate in the US; maybe it’s because society is collectively still a bit gun-shy when it comes to talking openly about period facts and myths. No matter the cause, it means that a lot of us (myself included) are still pretty confused about some of the nitty-gritty details of the menstrual cycle.

To help clear up a bit of the confusion, we asked nine health experts (OB/GYNs and nurses) to share the questions they get asked all. the. time. Chances are if they hear these questions on the regular, you’re probably wondering about them yourself, too.

1. “What is a ‘normal’ period?”

Honestly? It depends. “It is important to know that every [person] can have differences in their cycles that are routine and normal for them,” says OB/GYN Jyoti Desai, MD, FACOG, and an assistant professor at the University of Nevada, Las Vegas School of Medicine. What’s standard operating procedure for one person (some clotting, for example, or a period that lasts for just two days) isn’t necessarily “normal” for another person.

However, there are some general guidelines that can help a person determine whether or not their flow is normal for them. “Cycles that occur every 21 to 35 days and [periods that] last two to seven days are considered to be regular or normal,” says Dr. Desai. How much blood you shed can also be a helpful marker of normalcy. “The medical definition of a normal period is about 80 milliliters (five to six tablespoons) of blood,” says Lauren Nelson, MD, an assistant professor of obstetrics and gynecology at the George Washington School of Medicine and Health Sciences. “[However] the perception of bleeding too much is more important than the actual amount.” Read: If you feel like you’re suddenly bleeding more than normal during your period, talk to your doctor ASAP.

The duration of your cycle can also change over time, says June Gupta, NP, the associate director of medical standards at Planned Parenthood Federation of America, meaning what was normal for you when your first got your period can be different than what’s normal now. “During the first few years of your period, it might not always come at the same time every month. You may bleed more or less, or have different PMS symptoms,” Gupta says. “As you get older, periods usually get more regular and it’ll be easier to know what’s ‘normal’ for you.”

Not sure what your “normal” is? Try a period tracking app, says Karen Duncan, MD, an assistant professor in the department of obstetrics and gynecology at NYU Langone Health. “This is a great way to get a handle on your cycle and find out your typical cycle length,” Dr. Duncan says. “Tracking your cycle is also a great way to be aware of your most fertile days each month if you are trying to conceive; also good to know if you want to avoid pregnancy.”

2. “Why does birth control affect a person’s flow?”

First things first: Depending on the type of BC you use, it might not even be a “true” period. “Even though you have a period with hormonal birth control pill use, it isn’t a natural period, per se,” explains Stephanie McClellan, MD, chief medical officer for Tia Clinic.

Most birth control pills prevent pregnancy by preventing your ovaries from releasing an egg every month. (Without an egg, there’s nothing for a sperm to fertilize.) Per the American College of Obstetrics and Gynecology, the hormones released by the pill also thin the lining of your uterus. A “period” on this kind of birth control is called withdrawal bleeding, Dr. McClellan says, because it happens during the week on your birth control pack that you’re taking the placebo pills—your hormone levels drop, causing that thinner lining to shed. “The birth control pill bleeding is actually related to removing the hormonal support that the pill gives you every day,” she says.

If you’re using a long-acting, reversible contraception like the implant or a hormonal IUD, Dr. McClellan says you may experience some spotting or no bleeding at all. (For example, one in five people who have the Mirena IUD stop having periods altogether within a year of insertion.) The hormones in the IUD are thinning the lining of the uterus (similar to the pill), but the IUD releases hormones all the time—giving no opportunity for you to go through that “withdrawal.”

“In contrast, copper IUDs, which don’t have hormones, but work by sterile inflammation, cause heavier bleeding and more menstrual cramps,” says Dr. McClellan. Without hormones, there’s nothing at work to thin the lining of your period or otherwise prevent them from happening.

3. “How necessary are periods?”

Depends on who you ask. While some hormonal experts argue that periods are an important part of health for people who have uteruses, Karen Wang, MD, director of Johns Hopkins Medicine’s AAGL Fellowship in Minimally Invasive Gynecologic Surgery, says if you’re on hormonal birth control, a period is not necessary. “It’s okay if you use the pills continuously to suppress your cycles for longer than a month, or if you have a progestin IUD in place,” says Dr. Wang. “You do not need a period to ‘flush’ out the uterus.”

There are of course a lot of reasons why a person might not want to have a period in the first place. Women in the military often opt for IUDs or other long-acting forms of birth control that typically decrease period frequency since access to menstrual products can be difficult while on deployment. Transgender, gender non-conforming, or non-binary people might also choose to stop having their periods because just having it could trigger gender dysphoria (a psychological condition where a person has conflict between their gender identity and the one they were assigned at birth, which can result in self-esteem issues and other mental health issues like depression). 

If the whole “Why is my period necessary, anyways?” is something you’re struggling with—say you’re having particularly painful periods—definitely bring it up with your OB/GYN who can talk through with you what’s going on.

4. “Why are periods sometimes irregular?”

This is an important one to bring up with your doctor. “Irregular periods are not normal and can have many different causes,” explains Norbert Gleicher, MD, FACOG, FACS, founder of the Center for Human Reproduction. Per the NIH, an irregular period could mean having periods that occur more than 35 days apart, having super heavy bleeding or bleeding that lasts for longer than a week, or even unusual spotting before periods.

Dr. Gleicher says people who notice these kinds of changes in their periods should go talk to your OB/GYN as soon as possible. “Irregular periods do not automatically denote a medical problem, but should be investigated,” he says. Medical reasons for not getting a period could include perimenopause and polycystic ovarian syndrome (a health condition where a person has ovarian cysts, irregular menstrual cycles, and/or increased androgen levels), he says. Non-medical reasons include travel, particularly traveling across time zones, and too little body fat, which is common among competitive athletes.

5. “What does it mean if my period blood color changes?”

Don’t freak out too much about this one. While period blood color can offer some hints about what’s going on in your body, it’s generally not the most important metric for understanding overall period health. “The color of your period is probably the thing that matters the least,” explains Jennifer Conti, MD, an OB/GYN with Stanford Health Care. “We care way more about how often you’re bleeding, how heavy or light the flow is, and any related symptoms like pain, migraines, or mood symptoms. The color of the blood can vary depending on how fast or slow blood is in exiting your uterus, but it really has no clinical significance.”

FWIW, brown period blood is a pretty common color, Sherry Ross, OB/GYN, previously told Well+Good. “In the beginning, [menstrual] blood tends to be bright red in color, and as it comes to an end, appear brown or black,” she said. It’s typically just older blood that has oxidized, and is generally not anything to worry about.

6. “Why are periods so painful?”

Blame prostaglandins, says Jessica Shepherd, MD, medical advisor for Rory, an online women’s health service, and a gynecologic surgeon at Baylor University Medical Center. These hormones are made in the lining of the uterus and are involved with the body’s natural inflammatory and healing response. They also help regulate the menstrual cycle, ovulation, and even kick-start the labor process. 

“The [prostaglandin] levels are high in the beginning and decrease as the cycle continues, and typically, the pain decreases as the levels of prostaglandins decrease,” Dr Shepherd says. However, excessive pain that doesn’t seem to get better over the course of the period can be a sign that something’s off, she adds. “This can be an indicator of issues such as endometriosis, fibroids, or pelvic pain syndromes. That’s why it’s important to see your gynecologist when pain starts so there is a discussion on how to manage the pain and also to make sure there are no other underlying diseases.”

Real women share what they wish they knew before getting their IUD. And here’s how to embrace period positivity as an adult.