In the days leading up to their periods, about 75 percent of women suffer some permutation of the irritability, irrational overreactions, weepiness, mood swings and crabbiness that are the hallmarks of PMS. (The other 25 percent get to experience it secondhand.) Men use it as a catchall for bitchy behavior and we parlay the excuse as needed: I’m hormonal, back off. Now experts are exploring the possibility of another “that time of the month,” with potentially greater psychological implications.

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Researchers at the University College London are reporting that they have identified a narrow window of the menstrual cycle, just after ovulation, when women are at their most psychologically vulnerable. They took 41 women aged 18 to 35 who had regular cycles, and presented them with a graphic 14-minute film depicting real life scenes of death, mutilation and injury.

A third of the women were in the mid-follicular phase of their cycles (around day nine of a 28-day cycle), a third were in the early luteal phase, just after ovulation (around day 17), and the rest were in the late luteal phase, near menstruation (around day 24). The researchers instructed the participants to track any disturbing memories of the film that cropped up over the subsequent 72 hours.They found that women in the early luteal phase—which falls roughly 16 to 20 days after the start of their period—had more than three times as many intrusive thoughts as those who watched the video in other phases of their menstrual cycle. Lead researcher Sunjeev Kamboj, Ph.D., of UCL’s Department of Clinical, Educational and Health Psychology, believes this means there may be about five days within the menstrual cycle when a woman’s hormonal balance may leave her particularly vulnerable to experiencing distressing symptoms after a stressful event. This could mean an increased chance for depression or post-traumatic stress disorder (PTSD) following a difficult life event around the time of ovulation.

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“Whenever you have hormonal shifts, you will see people having less tolerance for stress, unable to cope as well with the stressors around them,” explains Lisa Robbins, M.D., a psychiatrist who specializes in women’s mental health related to hormonal issues. So, like PMS (which can start a couple days to a couple weeks before you get your period), hormones are driving an unusual and intense emotional response. But unlike PMS, if something stressful or traumatic happens in that window of vulnerability, negative psychological symptoms such as intrusive thoughts will not only affect you in that moment, but can continue to affect you throughout the luteal phase of your cycle. The symptoms may feel similar, but they are actually more akin to the flashbacks of PTSD than the hyperemotional eruptions of PMS.

Dr. Robbins recommends that all women track their cycles, in order to identify what phase they’re in and prepare mentally for intense emotional reactions that could catch them by surprise. There are apps such as Period Tracker and My Cycles that can make it easy. Calendaring your period and symptoms can help you find patterns and eventually predict when you are likely to start your period, as well as the days when you may be more susceptible to the effects of a stressful event.

Once you identify your vulnerable days, you may start to notice that you’re particularly sensitive right after ovulation or right before your period. Armed with that insight, you can take steps toward coping with the things that trigger you and try to preemptively de-stress. Mindful distraction (picking an activity and really getting into it), deep breathing, meditation or treating yourself to a massage can help you take control of your emotions and avoid ruminating on upsetting events. Paired with an awareness and understanding of your cyclical predispositions, these techniques can help with PMS symptoms, as well as prevent a stressful situation from turning into a persistent mental health issue.