Women across Russia, the United States and other countries reported unusual changes to their menstrual cycles in summer 2026, touching off online debate and a flood of competing theories.
Some said they had no period for an entire month. Others reported two in one month. The pattern spread quickly across social media, where it was dubbed the June phenomenon.
The discussion gained momentum when a TikTok creator known as @thrivingwithhannah asked her followers what was happening to their bodies in June. The post drew more than 45,000 likes and comments from women describing erratic bleeding, including one who said she feared she was entering menopause.
American endocrinologist Afrouz Demery ran an online survey through her Instagram account that drew 11,000 responses. She found that complaints about disrupted cycles were equally common among women in countries struck by unusual heat and those in cooler places such as Finland and Australia, where June falls in winter.
That result undermined the most popular theory, which blamed the European heat wave. Other explanations circulating online ranged from esoteric ideas about women synchronizing their energy to jokes that scientists at CERN had disrupted cycles by shutting down the Large Hadron Collider weeks before the reports began.
What doctors say
Doctors rejected all of those theories. Anna Tarasova, head of the Women’s Health Center at City Clinical Hospital and a candidate of medical sciences, said social media posts are not scientific research and the June phenomenon is a popular internet term, not a recognized diagnosis. Social networks allow people to share experiences rapidly but cannot establish how widespread a pattern really is or identify its cause, she said.
Tarasova also said that seeing a period twice in one calendar month is not necessarily abnormal. A healthy menstrual cycle can run anywhere from 21 to 35 days, meaning a woman with a shorter cycle might bleed early in a month and again near the end. What appears to be a second period, she added, can also be mid-cycle bleeding tied to hormonal changes, contraceptive use, stress, thyroid disease, uterine polyps, fibroids or early pregnancy.
Ekaterina Dragunova of the Semeynaya clinic network said there are no grounds for identifying a single shared cause and that the theory involving the CERN collider has no connection to medicine. She described the menstrual cycle as a sensitive system that responds to changes both inside the body and in the surrounding environment.
Anastasia Laskevich of Yusupov Hospital said extreme heat is a plausible contributing factor. She explained that sharp temperature swings and prolonged heat worsen sleep, raise cortisol levels, cause dehydration and trigger vascular spasms, any of which can push a cycle forward or back by a few days. Travel, jet lag and changes in daily routine during the holiday season can have similar effects, she said.
Doctors said a single unusual cycle is rarely a sign of serious trouble. They recommended consulting a doctor if disruptions repeat over several consecutive months, are accompanied by unusual bleeding or significant pain, or if pregnancy cannot be ruled out.
