Lanora Vasquez wasn’t at any of the protests against police brutality that spread through the city of Portland in summer of 2020. But she lived in Portland, near where the protests happened and where police officers regularly fired off canisters of tear gas. Gas doesn’t stay confined to one area — it spreads, and Vasquez says it spread into her home.

During and after the protests, Vasquez said she experienced changes to her menstrual cycle, including severe spotting and major cramping. She attributes those changes to tear gas exposure. And she isn’t alone: many other people in the city also reported menstrual cycle changes after exposure to tear gas, and many believe that the two are linked.

Michael Fuller, a lawyer in Portland, says he’s heard from dozens of people who’ve had similar experiences to Vasquez. He’s representing her in a lawsuit filed in December against the city of Portland alleging that the tear gas was responsible for changes in her menstrual cycle and asking for $10,000 in damages. “There’s just an overwhelming number of anecdotal cases,” Fuller says.

In fact, anecdotal reports have linked tear gas to menstrual changes for years. These changes aren’t benign — cramps can be debilitating, and because changes to menstrual cycles often indicate a medical problem, sudden differences can be distressing. Fuller believes people like Vasquez deserve to be compensated for their suffering, but he’s a lawyer, not a doctor. And he recognizes that, while lots of people may have had this experience, there still hasn’t been enough research to prove that tear gas directly causes menstrual changes. “Anecdotally, it’s obvious; scientifically, it’s less clear,” Fuller says.

The lawsuit underscores the disconnect between how discoveries are made in court and in the lab, especially when the legal system is asked to handle a still-unsettled scientific question. Even if the lawsuit is successful — indicating that yes, cities can be held responsible for menstrual cycle disruptions after their police departments use tear gas — it doesn’t change the fact that medical researchers still aren’t able to conclusively say tear cause caused the changes.

But if it’s successful, researchers say the lawsuit could help hold cities and police departments more accountable for the use of a dangerous chemical weapon and propel the work that’s looking for scientific clarity. Even with a legal decision, it’d still be important to make the scientific case, says Asha Hassan, a doctoral student and researcher at the University of Minnesota School of Public Health studying the link between tear gas and reproductive health.

“A higher caliber of evidence is always the best thing, regardless of what litigation happens,” she says. “That data is still needed.”

Prior to summer 2020, there were some sparse reports on the link between menstrual cycle disruption, miscarriage, and exposure to tear gas — mostly anecdotal information collected by human rights groups. There’s also been decades of research on animals showing that the way tear gas affects their bodies could impact hormone levels, says Juniper Simonis, an ecology and evolutionary biologist, toxicologist, and founding member of the Chemical Weapons Research Consortium in Portland. That could point to a biological mechanism for the menstrual changes people exposed to tear gas experience.

But there hadn’t been solid academic research looking at the question of how tear gas exposure impacts menstrual cycles in people. So in the aftermath of the 2020 protests, Hassan and a group of colleagues set out to conduct a more rigorous analysis.

The team surveyed over 2,000 adults exposed to tear gas in Portland during summer 2020. And they found that people exposed to tear gas said they had menstrual changes. The research, published in April 2021 in the journal BMC Public Health, found that the more exposure someone had to tear gas — a few days versus a single day, for example — the more likely they were to have menstrual disruptions like spontaneous bleeding or increased cramping.

This study still isn’t able to say that the tear gas is what directly caused the changes — the research simply uncovered a correlation. To establish a causal link, researchers would need to create controlled environments where people are exposed to tear gas and then track what happens to them after — an experiment that would never pass an ethics review board. That’s why researchers focus on tracking after events like protests.

To make matters more complicated, the exact components of tear gas are often murky, Hassan says. It’s considered proprietary information by companies, so scientists can’t untangle what chemicals specifically could be interacting with the body to produce the changes people are reporting.

Despite the limited research to date, causation is what Fuller’s case is trying to prove. He’s arguing that exposure to tear gas was responsible for his client’s menstrual changes. And scientific clarity may not be necessary for the lawsuit to be successful. He won’t need to prove to a scientific standard that exposure to tear gas caused his client’s menstrual cycle disruption. A jury would just need to decide if it was more likely than not that the tear gas was a substantial factor, and he’ll have experts who can testify in court that it was.

“It would certainly strengthen the case if it was generally accepted in the scientific community that there was a causal link between tear gas and interference with menstrual cycles,” Fuller says. “But we’re very comfortable with the level of evidence that we have.”

It’s not a level of evidence scientists would be comfortable using to say that there’s a cause-and-effect relationship here, though. “I can see some relationships between the two, but ultimately, I don’t think a successful trial would prove the case in the long run,” says Rohini Haar, research fellow in the Human Rights Center at UC Berkeley and medical expert with Physicians for Human Rights. “It would have to come from a scientific place for me.”

The gap between the evidence lawyers need and the evidence scientists need shows how differently each discipline tries to find answers. What convinces a jury doesn’t necessarily convince a scientist. And a jury agreeing that tear gas was responsible for menstrual changes would not be considered evidence for a causal link by researchers — they’d still have to run the experiments and pull the data.

But that doesn’t mean the groups are in tension or that a legal decision wouldn’t be helpful to scientific experts. (Right now, the city is pushing back on the suit and disputing the claim that tear gas could have traveled to Vasquez’s home, according to email correspondence between Fuller and the city’s attorneys.) A legal win could draw more attention to the harms tear gas can do, driving funding for more scientific research. If doctors know very little about how tear gas exposure relates to menstrual cycle changes, they know even less about the effects of living in areas that are impacted by tear gas, like Fuller’s client.

“What this kind of lawsuit can highlight is the need for continued work on the human impacts,” Simonis says. “This was someone who lived in the area. And we have no general understanding of the level of impact this could have on someone who lives in these areas.”

A win, and more legal action that builds on that precedent, could also open new avenues for experts to get information about tear gas through legal proceedings — like its exact chemical makeup, for instance. Having a clear understanding of the chemicals involved would help researchers try to figure out the specific ways tear gas affects the body, Hassan says.

In her view, the more focus on the issue, the better. “We are just touching the very tip of the iceberg here in trying to get a better understanding of what the relationship is between tear gas and health.”