PORTLAND (Oregon) • At some point last summer, there were just too many reports of protesters who had experienced abnormal menstrual cycles after being exposed to tear gas for Dr Britta Torgrimson-Ojerio to dismiss them as coincidence.
A pre-school teacher told Oregon Public Broadcasting that if she inhaled a significant amount of gas at night, she would get her period the next morning. Other Portland residents shared stories of periods that lasted for weeks and of unusual spotting.
Transgender men described sudden periods that defied hormones that had kept menstruation at bay for months or years.
Dr Torgrimson-Ojerio, a nurse researcher at the Kaiser Permanente Centre for Health Research in Portland, Oregon, decided she would try to figure out whether these anecdotes were outliers or representative of a more common phenomenon. She surveyed around 2,200 adults who said they had been exposed to tear gas in Portland last summer.
In a study published this week in the journal BMC Public Health, she reported that 899 of them - more than 54 per cent of the respondents who potentially menstruate - said they had experienced abnormal menstrual cycles.
"Even though we cannot say anything scientifically definitive about these chemical agents and a causal relationship to menstrual irregularities, we can definitively say that in our study most people who had menstrual cycles or a uterus reported menstrual irregularities after reporting exposure to tear gas," Dr Torgrimson-Ojerio said.
Downstream effects, like the impact on fertility, are not known, but "this is our call to action to ask our scientific community to turn their eye to this issue", she said.
Professor Kira Taylor, of the University of Louisville School of Public Health and Information Sciences, who is conducting a similar study, said Dr Torgrimson-Ojerio's study provided "some of the first solid evidence" that tear gas might be linked to menstrual abnormalities. It is also "the first study to document the longer-term effects of tear gas exposure in a large population", she said.
Dr Sven-Eric Jordt, a professor of anaesthesiology, pharmacology and cancer biology at the Duke University School of Medicine, who was not involved in the study, said most of the research that police agencies and the government rely on to inform them about tear gas safety "are outdated, often 50 to 70 years old, and don't measure up to modern toxicological approaches".