You know why you have to poop so much during your period and that PMS isn't all in your head. But there's another super-fun (not) thing about that time of the month you might have always wondered about, and that's why period blood smells so ... weird and unlike regular blood. Now, we've got the answers.

In an interview with Refinery29, Taraneh Shirazian, MD, assistant professor in the department of obstetrics and gynecology at NYU Langone Joan H. Tisch Center for Women's Health in NYC, spilled the real deal about period blood smells. Here's what Seventeen.com learned:

1. Period blood isn't all blood. Menstrual fluid is filled with bacteria, vaginal mucus, and tissue (you know, since you're shedding the lining of your uterus.) How strong the odor is depends on how long the blood is in your uterus, Dr. Shirazian explains to Refinery29.

2. It shouldn't smell fishy. "When you're bleeding, you retain moisture in the vagina," says Dr. Shirazian. This could lead to "secondary vaginal infections like bacterial vaginosis, which has a strong, fishy odor." BV is caused by changes in the amount of certain types of bacteria in your vagina, according to Womenshealth.gov. It's not an STI, but it can raise your risk of getting an STI. It's treatable with antibiotics, so make sure to check with your doctor. Dr. Shirazian recommends keeping everything as dry as possible down there, so change pads, tampons, and menstrual cups often.

3. Douching can make odor worse. Don't worry about normal vagina odors, period blood, or discharge, and do not ever douche. Douching can actually cause infections, like BV, and is associated with higher rates of pelvic inflammatory disease. Just wash with mild, scent-free soap or water, and you'll be fine.

From: Seventeen
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Elizabeth Denton
I'm Liz, the fashion and beauty girl at Seventeen.com. I'm basically a human guinea pig, testing every beauty product that comes into the office and changing my hair all the time. I love cats (even though allergic) and I can't read enough YA novels.