Viral period trends, checked

A claim is not the same as a study. This Column takes six period claims you may have seen online. Each claim gets the same three parts: the claim, in plain words; what research says so far, with the kind of study named; and who to ask. The order is for easy reading. It is not a ranking. For most of these claims, the research so far is small or inconclusive, or we found no study at all.

1 · “Eat and exercise by your cycle phase, and you’ll do better”

The claim. Researchers describe cycle syncing as “a trend that involves harmonizing daily activities and self‐care rituals with various stages of the menstrual cycle”. In a study of 100 TikTok videos collected in January 2023, “More than half of the creators recommended aligning diet and exercise with the four menstrual cycle phases.”

What research says so far. On strength training, a 2023 umbrella review led from McMaster University, in Hamilton, Ontario, looked at the published reviews. In the authors’ opinion, “it is premature to conclude that short-term fluctuations in reproductive hormones appreciably influence acute exercise performance or longer-term strength or hypertrophic adaptations” to resistance training. They also noted “poor and inconsistent methodological practices” in the studies. That review is about strength training only. It says nothing about food, mood or schoolwork. Another research team calls the clinical research on cycle syncing “inconclusive”.

Researchers have also studied the videos themselves. In the 2023 sample, “About one‐third of creators provided credentials. However, very few mentioned scientific evidence.” The authors concluded that the content “oversimplifies a complex literature”. A 2026 study looked at 160 cycle-syncing workout videos, with 18.9 million views in total. It found that 9% were posted by healthcare providers, 98% were positive about cycle syncing, and the videos were “of poor educational quality”. It also found that “80% of videos promoted a product through affiliate marketing”.

“Inconclusive” does not mean your cycle never matters. It means research hasn’t shown that planning by phase does what the videos say.

Who to ask. A doctor, a nurse practitioner or a school nurse.

A note on words: some sources we quote here say “women” or “PCOS”. We keep researchers’ words so we report their findings accurately. In our own words, we say PMOS, the condition’s new name. The Reading Room is for everyone who menstruates.

2 · “Eating certain seeds in each phase balances your hormones”

The claim. A 2025 review defines seed cycling as “a dietary strategy involving flax, pumpkin, sesame, and sunflower seeds consumed in specific phases of the menstrual cycle.”

What research says so far. That review is a systematic review. It found 10 studies, with 635 people in total. The people studied had PMS or PMOS (formerly PCOS). In the studies, seeds were given “either individually or as part of a seed cycling protocol”.

The review reports that, in these studies, seeds were associated with some improvements, such as in PMS symptom scores, cycle regularity and some hormone measures. The authors say this conclusion “is based on small sample sizes and moderate-quality evidence”. They call for “larger randomized controlled trials and standardized intervention protocols”. They also note that “adherence to seed intake protocols was not objectively verified”.

Who to ask. A doctor or a nurse practitioner. The studies did not check how seeds might interact with medicines or hormone treatments.

3 · “There’s a flu you get before your period”

The claim. Some videos describe a “period flu”: feeling achy, tired or unwell in the days before a period.

What research says so far. “Period flu” is not an official medical diagnosis. An ob/gyn quoted on a US hospital’s health site says: “Period flu isn’t the flu or an official medical diagnosis. It’s a type of premenstrual syndrome (PMS), which can cause symptoms similar to the flu.” The same page says prostaglandins made by the uterus “can also cause diarrhea, nausea and sometimes even a low-grade fever before your period.”

In Canada, the Society of Obstetricians and Gynaecologists of Canada (SOGC) does not use the words “period flu” on its PMS page. It lists physical symptoms of PMS that include “Muscle aches”, “Joint pain”, “Headaches” and “Low energy, fatigue”. It says: “Most women experience some symptoms in the days before their period starts.” The UK’s NHS says PMS “can affect anyone who has periods”.

Who to ask. The SOGC says: “It is important to see your doctor if you suspect you may have PMS.” This Column can’t tell you what your own symptoms mean. If you feel unwell and are not sure why, a healthcare provider or your provincial health line can help.

If you use tampons, one more line matters. Health Canada says the initial symptoms of toxic shock syndrome (TSS) “are similar to the flu, and can include high fever, nausea, vomiting, diarrhea, dizziness, fainting, and disorientation.” It says: “If you have any of the symptoms of TSS when using a tampon, remove it and get immediate medical help. If you can’t reach your doctor, go to the nearest Emergency Care facility.” More in “TSS: the facts, calmly”.

4 · “Period blood is a natural face mask”

The claim. A US dermatology clinic lists what people say menstrual masking does: “glowing skin”, clearer “pimples or blemishes”, and “anti-aging effects from ‘stem cells’”. It notes the practice is framed as “a natural, body-positive ritual”.

What research says so far. We searched PubMed, a large public database of medical research, in September 2026. We found no peer-reviewed study of menstrual masking. The same clinic says: “There are no clinical studies showing that topical menstrual blood improves acne, wrinkles, glow, or texture.” It also says that putting “non-sterile bodily fluid” on the skin brings bacteria, yeast and “Potential pathogens” to it.

Online, it is often framed as body-positive. The Reading Room shares the wish to end shame about periods. The question here is only what the research shows, and so far we found none.

Who to ask. For a question about your skin, a doctor or a nurse practitioner.

5 · “You can’t swim on your period”

The claim. You have to stay out of the water during a period.

What research says so far. SickKids, the Toronto children’s hospital, says: “People who menstruate can still enjoy swimming, running and all of their normal activities.” For each format and the water, see “Can you swim on your period?” in the Reading Room.

Who to ask. A parent or carer, a school nurse, or a doctor.

6 · “Friends who live together get their periods at the same time”

The claim. People who live or spend a lot of time together start to have their periods on the same days.

What research says so far. Researchers call this “menstrual synchrony” and have studied it since the 1970s. A 2006 study followed 18 pairs and 21 groups of three students living in dormitories for five months. It found that “menstrual synchrony was not found”. The author wrote that there was “still no conclusive evidence for the existence of this phenomenon.” That is one study, with its own summary of earlier work. Put simply: studies have not confirmed it.

Who to ask. No one needs to, unless your cycle worries you. Then, a doctor, a nurse practitioner or a school nurse.

What this is not

This Column reports what researchers, a children’s hospital, health bodies, a hospital’s health site and a dermatology clinic say, dated, in their own words. It does not judge anyone who tried a trend. It does not say any trend is right or wrong for you. It does not suggest a diet, a supplement, an exercise plan or a product.