Debunked: 5 Myths About Menstrual Cups

There are so many myths about menstrual cups and menstruation. Does the blood flow back into the womb when the cup is full? Is it true that virgins can’t use period cups? We put all the facts on the table and gathered the most common myths and truths.

Separate the fact from the fiction

1. MYTH: When the cup is full, the blood flows back into the uterus.

TRUTH: Wrong! The blood flows into the vagina and thus into the cup through the tiny hole in the cervix. It is not possible for the blood to flow back into the womb, not even if you're upside down. The muscles of the uterus push the menstrual blood out actively from the uterus.

2. MYTH: You can't use a menstrual cup if you have endometriosis.

TRUTH: Wrong! It is completely safe to use a menstrual cup if you have endometriosis, just ask your doctor first! Read our article ‘What is endometriosis?

3. MYTH: Virgins cannot use menstrual cups.

TRUTH: Wrong! Even people with a uterus who have not had penetrative sex can use the cup. The vagina may occur ‘narrower’ with a virgin vagina, and the hymen may still be present, but these facts do not prevent the use of the cup. At most they'll bring light challenges the first few times of inserting the cup.

4. MYTH: You can go pee/poo or use the toilet while having a menstrual cup inserted.

TRUTH: True! With the cup inserted, you can easily go to the bathroom. This is two of the most common questions we get asked, can you pee with a menstrual cup in? Or can you poop with a menstrual cup in? Of course the answer is yes, you just need to make sure it's not out of place, like during a bowel movement. Good hygiene is essential so that no foreign bacteria enter the vagina or cup. If you want to make sure you're comfortable and clean, remove the cup before going to the toilet and wash your hands (and down there) carefully before inserting the clean cup. You can empty the cup as often as you'd like!

5. MYTH: You don’t need to boil your menstrual cup after every cycle

TRUTH: Sort of. Your menstrual cup does not necessarily have to be boiled every cycle (although we highly recommend it). However, before you use your cup for the first time, make sure to boil it for 20 minutes. Read our article ‘How to clean’ for full instructions. After your first use, boiling it for 10 minutes is good enough. Keep an eye on your menstrual cup when you boil it, you wouldn't want it to forget about it and have it burn at the bottom of the pot! Whatever you do, do not use a hand sanitizer. You can buy cup wipes that are specifically designed for menstrual cups, with no colorants, oils or scents that could damage the silicone. And don’t forget good hand hygiene!

If you’ve still got a question, or want to read more about the things people are curious about, check out our article ‘Everything you’ve ever wanted to ask your OB/GYN’. Alternatively check out our menstrual products.


Hi Aimee,
thanks for your question! The menstrual cycle is regulated by hormones (read more here: and the cup does not contain hormones, so it cannot delay/prevent your periods.
Do you mean that when you insert the cup and remove it there is no blood inside the cup, but as soon as you remove the cup the flow starts?
Best regards, Team Lunette

Lunette Cup February 10, 2023

Question: I’ve been using a cup for several years and come to wonder- can inserting your cup ahead of actual flow delay your period? Or is that just in my head? My periods are pretty regular (though heavy) with fairly trackable onset symptoms, but it seems like everytime I’m actually fully prepared, I have to take my cup out again for flow to start. What’s going on here?

Aimee February 10, 2023

Hi M. Hargrove, thank you for your comment! We’re terribly sorry to hear about the kidney stone! It is definitely very important to be able to empty the bladder fully when using a menstrual cup. What type of cup were you using? A smaller or softer cup could work better so that it isn’t putting pressure on your bladder or urethra. This way you could still enjoy a pad-free period. :)
-Team Lunette

Lunette Menstrual Mentor August 16, 2021

I just had to stop using my cup. It impeded the flow of urine so I wasn’t emptying my bladder when I went to pee. Didn’t seem like a big deal until I got a kidney stone and the urologist pointed out that not emptying your bladder all the way can cause kidney issues. So I am back to using pads which give me a rash. It was a wonderful 2 years without the mess of pads.

M. Hargrove August 16, 2021

Hi Muchi! With a little practice you’ll be able to remove the Cup without mess ☺️. Use the stem as a guide to reach the bottom, pinch the bottom with you thumb and fore finger, and gently wiggle the Cup out!
-Team Lunette

Lunette Menstrual Mentor November 23, 2020

When taking out the menstrual cup, wouldn’t the blood in the cup be kinda pushed back up and leak out because the cup would be squeezed by the entrance of your vagina when taking it out?

Muchi November 23, 2020

Hi Emily! Yes, you can! If you run into any issues we’re always happy to offer troubleshooting tips – just email us at and our Menstrual Mentors will get right back to you. <3
-Team Lunette

Lunette Menstrual Mentor November 10, 2020

Hi Kittu! Yes, you can! <3

Lunette Menstrual Mentor November 10, 2020

can we pee and poo with cup inside our body?

kittu November 10, 2020

Can I lay down in any positions with my menstrual cup like laying down on my side, belly and back?. And if I sit down does it leak?.

Emily November 10, 2020

There is no way I could boil my cup in my crowded, multi-family home (where I’m the only female…) – is cleaning with lunette wipes and/or soap and warm water good enough?

Anon November 10, 2020

Hi, Kiasia! Yes, you can lay on your side while on your period. :)
-Team Lunette

Lunette Menstrual Mentor September 24, 2020

Can you lay on your side when you on your period

Kiasia September 24, 2020

Can you lay on your side when you on your period

Kiasia September 24, 2020

Hi, Kylie! Sorry to hear that! Please contact us at and our amazing Menstrual Mentors are happy to assist with troubleshooting this issue. :)
-Team Lunette

Lunette Menstrual Mentor September 23, 2020

While wearing my cup I get bad tummy pains when needing to poop

Kylie September 23, 2020

It is recommended to use a small cup from my age group but I have heavy flow. Will the cup leak if it is full? For example if I sleep with my cup in on my heavy days will I wake up with blood leaking all over?

Drush August 24, 2020

Hi Anonymous! Blood will not flow back into the uterus once it has passed through the cervix. You can wear your cup while swimming and diving, it cannot get lost inside. :) Just be sure to use your pelvic muscles to push the cup lower when removing, that way you’ll be able to reach it easier. <3
-Team Lunette

Lunette Menstrual Mentor August 05, 2020

If I go upside down will the blood come back into me? Also I do diving and can I wear a tampon or cup while diving or will it get stuck up there from the impact and pressure.

Anonymous August 05, 2020

Hi, Mysti! There are a couple of reasons that can cause the cup to slide down. The most common ones are:
*the cup is not completely open and has not created a good seal

the cervix comes lower during periods and may be pushing the cup out
*your pelvic muscles cannot hold the cup in place

Don’t hesitate to contact us at and we’re happy to troubleshoot further!

-Team Lunette

Lunette Mentrual Mentor July 10, 2020

what would cause a cup to fall out? I was asleep, woke up after 8 hours, I had very bad cramps, went to the restroom ( my urge to urinate was worse than to immediately remove the cup) I wiped and just as I was about to stand up, the cup fell out into the toilet. It was not hanging out, I didn’t feel it when I was wiping. What would make this happen?

Mysti July 10, 2020

Hi Lucky,

Thanks for your question! It’s possible for the cup to leak in any position, sleeping, sitting, or standing up. This can happen if the cup does not have a proper seal. If you’re experiencing leaking don’t hesitate to reach out at so we can help troubleshoot the issues you’re having! :)

Team Lunette

Lunette Menstrual Mentor December 15, 2019

When I lay flat on my back, side, or stomach to sleep while wearing the cup, is it possible for blood to seep out? Also if it is not possible, does the blood stay in the cup?

Lucky December 15, 2019

Hi Anonymous,

If neither one of you is suffering from any type of vaginal bacterial or yeast infection, then 20 minutes of boiling together should sterilize both cups sufficiently to be safe to use. Even though medical grade silicone is a very unfavorable platform for bacteria and yeast to live, it is still possible they will live after boiling- therefore, if either one of you is treating an infection and there is a change this bacteria or yeast was on a cup when they were boiled, it is possible that bacteria could have been transferred.

Hope this helps!

Team Lunette

Lunette Menstrual Mentor December 01, 2019

Hi there,

I boiled my friend’s and my own lunette together, in the same pot. It occurred to me later that germs could probably be shared this way. Is this something I need to be concerned about?

Thank you!

Anonymous December 01, 2019

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