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By now you've probably heard a lot of different things about your period. While some are clearly old wives' tales, others can be trickier to decipher. Whether you're wondering if it's safe to skip the Pill's placebos or if women in close proximity really do sync up their cycles, we've called in the experts to get to the bottom of some of the biggest menstruation myths out there.

1. Your hormones shift every seven years?
There's no such timetable. Your hormones are always shifting because that's what happens throughout the monthly cycle itself. But big-picture changes are also always going on. "Women's hormones are always shifting because the ovarian reserve [the supply of remaining eggs] gets lower and lower as we age," Nanette Santoro, MD, professor and chair of obstetrics and gynecology at the University of Colorado at Denver. The number of eggs in your ovaries in turn affects hormone levels. Specifically, as the number of eggs shrinks, levels of follicle-stimulating hormone (FSH)—which helps prompt ovulation—go up. And this can cause your periods to go out of whack.

2. Women who live together often get their periods around the same time?
Yes, and it has to do with pheromones, odorless chemicals that women produce and release. The theory is that our bodies detect and respond to the pheromones of the women around us, and gradually this creates a synchronicity of menstrual cycles. Strangely primitive, but true!

3. You can't get pregnant during your period?
It's unlikely, but not totally impossible. Sperm can, in rare instances, wait for an egg for up to a week. If you have a very short or long cycle, ovulation can happen soon after, or even during, the bleeding phase, which gives sperm the chance to get lucky.

4. It's not safe to take the Pill without a break?
Not true. If you've been getting your period regularly and you don't want to, it's fine to skip it by taking the Pill continuously (no seven-day gaps). Because the Pill contains progesterone-like hormones, it prevents the growth of the uterine lining, so there's no buildup and no lining to be shed. That's why you won't get a period "There is no need healthwise to physically get a period," Dr. Santoro says. What is dangerous is if the lining of your uterus builds up and doesn't shed, since this can put you at risk for a buildup of precancerous cells. So if you're not getting periods and you're not on the Pill, menstruation should be induced at least every three months, says Sharon Mass, MD, a clinical assistant professor of obstetrics and gynecology at UMDNJ in Newark, New Jersey.

5. Men can get PMS? No. Men do have their own hormonal rhythms, but not monthly ones like women's. And "their hormones don't fluctuate significantly until they begin to lose testosterone in their 60s," says Michele Curtis, MD, an associate professor of obstetrics and gynecology at the University of Texas Houston Medical School.

6. If your mother got severe menstrual cramps, you're likely to get them, too?
Possibly. Doctors say they have seen a generational link, but it isn't clear whether it's conditioning, genetics or both. For some women, "it may have to do with attitude and expectations," says Dr. Curtis. So if you grew up hearing your mother complain about cramps and saw her spend days in bed during her period, you might be more attuned to menstrual pain yourself. But there's no question: "For some women, severe cramping can be very debilitating," says Dr. Curtis. "It's almost like they're going through labor every month." If this happens to you, talk to your doctor about taking oral contraceptives (they can make your periods lighter and less crampy since they stop the uterine lining from getting so thick) or prescription-strength pain relievers.

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