For decades, a fascinating idea has circulated among women: that those who live in close proximity will eventually find their menstrual cycles synchronising. Known as menstrual synchrony, this concept has been widely accepted as fact by many. However, scientific evidence now firmly debunks this long-held belief.
The Origins of a Persistent Myth
The theory of menstrual synchrony first gained significant attention in the early 1970s when Dr Martha McClintock published her groundbreaking study. Her research observed students sharing a college dormitory and suggested that women in close quarters experienced a convergence of their menstrual cycles. This phenomenon became known as the McClintock Effect.
Several subsequent studies during the 1990s appeared to support McClintock's findings, with some researchers proposing that olfactory cues or pheromones might be responsible for accelerating or delaying menstrual cycles to create this synchronisation effect.
What Modern Research Reveals
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, confirms there isn't a biological mechanism for menstrual syncing. The body simply doesn't work that way, despite how comforting the idea of connection through synchronisation might be.
Why The Belief Persists
So why do so many people remain convinced their periods have synced with friends or family members? Experts point to information biases and statistical probability rather than biological reality.
We're more likely to notice and remember when our cycles align with those we're close to, while overlooking the many times they don't match. With menstrual cycles varying in length and timing, it's statistically inevitable that cycles will overlap periodically purely by chance.
Studies confirm that cycles sync up at the same rate we would expect based on mathematical probability alone.
What Actually Affects Menstrual Cycles
While synchronisation with others isn't real, numerous factors do influence menstrual cycle timing and duration:
Body composition: Higher BMI is associated with irregular cycles.
Age: Cycles can be irregular during adolescence and approaching menopause.
Psychological stress: Depression can disrupt menstrual patterns.
Medication including birth control, and medical conditions like thyroid disease or PCOS.
Lifestyle factors such as smoking, alcohol and caffeine consumption, diet and physical activity levels.
Beyond Synchrony: Other Menstrual Myths
Medical professionals note that menstrual synchrony is just one of many misconceptions about periods. Dr Salena Zanotti highlights cultural myths portraying periods as dirty or embarrassing, while also dismissing the false idea that using tampons or menstrual cups affects virginity.
Dr Jensen confirms that both sex and exercise are safe during menstruation, though she notes that STI and pregnancy risks still exist during this time. Exercise may actually help alleviate period symptoms like cramps and mood changes.
Meanwhile, genuinely important menstrual health issues receive less attention. Dr Kling reveals that up to 85% of women experience some menstrual-related syndrome, with 40% reporting significant bother from their symptoms.
Conditions like painful periods (dysmenorrhea), abnormal uterine bleeding, and premenstrual symptoms are common yet often under-discussed. Dr Zanotti emphasises that periods don't have to be overwhelmingly painful or heavy, encouraging those who struggle to seek medical guidance.
While the myth of menstrual synchrony is relatively harmless, Dr Jensen cautions that following inaccurate health advice can have serious consequences. She recommends consulting healthcare providers before acting on health information from social media or friends.
