The billowing clouds of tear gas that the authorities are sending through protest crowds across the United States may increase the risk that the coronavirus could spread through the gatherings.

Along with the immediate pain that can cause watering eyes and burning throats, tear gas may cause damage to people’s lungs and make them more susceptible to getting a respiratory illness, according to studies on the risks of exposure. The gas can also incite coughing, which can further spread the virus from an infected person.

Sven-Eric Jordt, a researcher at Duke University who has studied the effects of tear gas agents, said he had been shocked to watch how much the authorities had turned to the control method in recent days.

“I’m really concerned that this might catalyze a new wave of COVID-19,” Jordt said. The virus has been linked to more than 106,000 deaths in the United States.

The protests after the death of George Floyd in Minneapolis have already raised alarm among health experts who have watched as protesters gathered by the thousands in cities around the country. While some demonstrators have worn masks and gloves, the crowds have often involved shouting and chanting in close quarters — a risky activity for a virus spread by respiratory droplets.

But the addition of wafting gases, which have been used widely by police forces in recent nights, has added an uncertain new element of risk to the scene.

In research conducted by the U.S. Army, examiners looked at the effects of exposure that thousands of Army recruits had to the common riot-control agent known as CS gas or tear gas. The study conducted in the summer of 2012 found that the personnel in a basic training cohort had a substantially high risk of being found to have an acute respiratory illness in the days after exposure than the days before.

The risk increased the more people were exposed, the researchers said.

The miserable initial effects of tear gas — including stinging in the eyes and throat — typically lasts for only 15 to 30 minutes after a person who has been exposed gets to an area with cleaner air. But many of the illnesses in the Army research surfaced days after exposure. Researchers cautioned that illnesses were not lab-checked, and could have been caused by damage to the respiratory tract rather than infection, or could have been prompted by other factors.

A study in Turkey examining the long-term effects of tear gas found that people who had been exposed had a higher risk for chronic bronchitis.

Tear gas has been around for decades, used around the world as a riot-control tool, including in Hong Kong during recent uprisings there. Treaties prohibit its use during war.

Jordt said he worried that the effects on healthy, young military recruits may also not fully capture the risks to people who are older or have underlying conditions. He said more research was needed on tear gas generally, since much of the research was decades old, but that it had been difficult to get funding to examine the issue.

The protests after Floyd’s death have focused on the disproportionate effects of police killings on black Americans, with protests led by groups such as Black Lives Matter. People of color have also been hit particularly hard by the coronavirus pandemic, with higher rates of hospitalizations and deaths than white people.

Researchers have long found that smoking can cause damage to upper airways and increase the risk of lung infections. The Centers for Disease Control and Prevention has said that conditions such as asthma and chronic lung disease can increase the risk of someone getting a severe coronavirus illness.

The CDC has said that prolonged exposure to riot-control agents may lead to long-term effects to eyes and breathing problems such as asthma.

The use of tear gas to disperse protesters has been the subject of criticism from organizations such as the American Civil Liberties Union.

Jamil Dakwar, the director of the ACLU’s Human Rights Program, said tear gas had become an overused tactic that could actually increase the volatility of a situation. He said the weapons that were so indiscriminate should not be used for dispersing people or in protests.

“It has become a first-resort weapon rather than a last resort,” Dakwar said.

Dakwar said he would like to see state and federal legislation that would restrict the use of those techniques. While the ACLU was not advocating an outright ban, he said the priority should be on de-escalation techniques.

Dakwar said the gas was so indiscriminate that he also worried about the health effects on police officers.