At some point last summer there were just too many reports of protesters having abnormal menstrual cycles after exposure to tear gas for Britta Torgrimson-Ojerio, a nurse researcher at the Kaiser Permanente Center for Health Research in Portland, to dismiss them as a coincidence.
A preschool teacher told Oregon Public Broadasting that if she inhaled a significant amount of gasoline at night, she would get her period the next morning. Other Portland residents shared stories of week-long periods and unusual spots. Transgender men described sudden periods defying hormones that had kept menstruation in check for months or years.
Dr. Torgrimson-Ojerio decided that she would try to find out if these anecdotes were outliers or representatives of a more common phenomenon. She interviewed 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 percent of those who may be menstruating – reported having experienced abnormal menstrual cycles.
"Although we can't say anything scientifically proven about these chemical agents or a causal relationship with menstrual disorders," said Dr. Torgrimson-Ojerio, "We can definitely say that in our study, most people with menstrual cycles or a uterus reported menstrual irregularities." after reporting exposure to tear gas. "
Downstream effects such as fertility effects are not known, but "this is our call to action to ask our scientific community to address this issue," she said.
Dr. Torgrimson-Ojerio was also interested in whether people had other problems more than a few hours after exposure to tear gas. She found that 80 percent of respondents had difficulty breathing, which was one of the most common complaints.
Kira Taylor, a professor of epidemiology and population health in the University of Louisville's School of Public Health and Information Sciences who is doing a similar study, said Dr. Torgrimson-Ojerio's study provided "some of the first solid evidence" for tear gas to be associated with menstrual irregularities. It is also "the first study to document the longer-term effects of tear gas exposure in a large population," she said.
Sven-Eric Jordt, Professor of Anaesthesiology, Pharmacology and Cancer Biology at Duke University Medical School, who was not involved in the study, welcomed the work.
Most of the research that police and government use to educate them about tear gas safety "are out of date, often 50 to 70 years old, and inconsistent with modern toxicological approaches," he said. "Most of these studies were conducted on young healthy men at the time, either in the police force or the military, not women or a general civilian population representing protesters."
Dr. Torgrimson-Ojerio and her colleagues recruited survey participants through social media and links on The Oregonian and Oregon Health Authority websites in July and August.
The researchers asked participants to explain exactly how their periods had affected after exposure to tear gas. Increased cramps, unusual spotting, and unusually intense or prolonged bleeding were the most common reactions. A number of people who normally don't have periods because of hormone therapy or age have reported unexpected bleeding and spots, said Dr. Torgrimson-Ojerio.
This study has limitations. It is not a random sample.
"It is possible that people who felt that their health was harmed by tear gas were more likely to react than people who were also exposed but did not have such harmful effects," said Dr. Taylor. "This means that some of the numbers may be exaggerated."
Because the subjects were allowed to participate anonymously, the researchers were unable to verify their accounts.
Nor can the study answer how or why tear gas may contribute to menstrual disorders, or the extent to which other factors are involved. The authors acknowledge that, for example, the high levels of stress and anxiety among protesters may also have contributed to the physical response.
"It is possible that pain, stress, dehydration and exertion play a role," said Dr. Jordt. Alternatively, tear gas can act as an "endocrine disruptor" and impair normal hormone function.
"The tear gas agent CS, which is sometimes used by the police, is a chlorinated chemical compound and creates additional chlorinated by-products when burned in the canisters used by the police," he said. "Exposure to chlorinated chemicals can affect menstrual health."
Alexander Samuel, a molecular biologist in France, has been researching similar issues since French protesters reported menstrual disorders.
He mentioned two additional areas for research: whether tear gas is metabolized to cyanide, which can lead to heavy menstrual bleeding, and what role a traumatic event can play in changing menstrual cycles.
Suspicions of tear gas and menstruation arose more than a decade ago during the Arab Spring protests, noted Dr. Jordt firmly.
In 2011, Chile also banned the use of tear gas after a study found that CS gas could cause miscarriages and harm young children. Three days later, Chilean police lifted the ban and insisted that the type of tear gas used was completely safe.