For decades, a peculiar belief has circulated among women: that when they live or spend significant time together, their menstrual cycles begin to synchronise. This phenomenon, known as menstrual synchrony, has been widely accepted as fact, but what does the science actually say?
The Origins of a Persistent Myth
The concept of menstrual synchrony first gained scientific credibility in the early 1970s when Dr Martha McClintock published her groundbreaking study. Her research observed students living in a college dormitory and concluded that women sharing close quarters experienced a convergence of their menstrual cycles.
This finding became known as the McClintock Effect and was supported by several subsequent studies throughout the 1990s. Some researchers even suggested that olfactory cues or pheromones might be responsible for accelerating or delaying cycles to create this apparent synchronisation.
Modern Science Debunks the Myth
More recent and rigorously designed studies have generally failed to demonstrate any actual synchrony between menstrual cycles of women living together, according to Dr Jewel Kling, chair of women's health at the Mayo Clinic in Arizona.
Dr Rachel Jensen, Darney-Landy fellow at the American College of Obstetricians and Gynecologists, states unequivocally: "There isn't a biological mechanism for menstrual syncing." The body simply doesn't work that way, despite the appealing nature of the concept.
Why Does the Belief Persist?
Dr Salena Zanotti, OB-GYN at the Cleveland Clinic, acknowledges that "many women think this is true." The persistence of this belief stems from psychological factors rather than biological ones.
We're more likely to notice and remember when our cycles align with those we're close to, creating confirmation bias. Additionally, with menstrual cycles varying in length and timing, mathematical probability ensures that cycles will occasionally overlap purely by chance.
What Actually Affects Menstrual Cycles?
Experts identify several genuine factors that influence menstrual cycle timing and duration:
- Body composition and BMI
- Age, particularly during adolescence and perimenopause
- Psychological stress and depression
- Medications including birth control
- Medical conditions like thyroid disease or PCOS
- Lifestyle factors including smoking, diet, and physical activity
Beyond Synchrony: Other Common Menstrual Myths
Menstrual synchrony isn't the only misconception surrounding periods. Many cultural myths persist, including the idea that periods are dirty or embarrassing, or that using tampons or menstrual cups affects virginity.
Dr Jensen confirms that both exercise and sex during menstruation are safe, though she notes that risks of STIs and pregnancy still exist during this time. Exercise may even help alleviate symptoms like cramps and mood changes.
Meanwhile, genuine menstrual health concerns often go under-discussed. Dr Kling reveals that up to 85% of women experience menstrual-related syndromes, with 40% reporting significant bother from their symptoms.
Dr Zanotti emphasises that "periods are a normal way of life" and shouldn't be overwhelmingly painful or heavy. She encourages anyone struggling with their cycle to consult a healthcare provider for management strategies.
While the myth of menstrual synchrony is relatively harmless, Dr Jensen cautions that following inaccurate health advice can have serious consequences. She recommends verifying health information from social media or friends with medical professionals before acting on it.
