There is still a lot of uncertainty about the coronavirus, but one thing we know is that it attacks the lungs. That’s why a growing number of doctors and public health officials are urging people to stop vaping and smoking of tobacco or marijuana products during the pandemic.

“It’s the sensible thing to do to reduce your risk,” said Dr. Stanton Glantz, director of UCSF’s Center for Tobacco Control Research and Education. “Based on what we know about smoking and vaping, it has a whole range of adverse effects on your respiratory system that increase the likelihood of you getting infected.”

While few studies have outlined the direct correlation between COVID-19 and smoking, there is evidence that cigarettes weaken the immune system and limit lung function. A UCSF study published in December said that people who smoke e-cigarettes also face a significant risk of developing severe, chronic lung illnesses — such as asthma, bronchitis and emphysema.

“Those are the kinds of things that would make this disease worse,” Glantz said.

He echoes advisories from the Food and Drug Administration, whose spokeswoman, Alison Hunt, said, “People who smoke cigarettes may be at increased risk from COVID-19, and may have worse outcomes from COVID-19,” and the National Institute on Drug Abuse, whose director, Nora Volkow, warned that the coronavirus “could be an especially serious threat to those who smoke tobacco or marijuana or who vape.”

A study published by the Chinese Medical Journal found that COVID-19 patients who had a history of smoking were 14 times more likely to develop pneumonia.

Of particular concern is the CDC report that those age 20 to 44 make up a big part of COVID-19 hospitalizations in the United States.

Noting the spike in youth infections, the World Health Organization said smokers significantly increase their chances of getting the virus through hand-to-mouth transmission, while sharing water pipes can transmit respiratory particles between people.

“Smoking and vaping means you’re touching your face — it means you are putting your hands near your mouth,” Glantz said. “That’s bad.”

Cigarettes and e-cigarettes release ultrafine particles, industrial solvents and various irritants into your airway that disable the cilia, the very small hairlike strands in the lungs and respiratory tract that filter out toxic material.

“That’s your first line of defense pushing the virus out of your body,” Glantz said. “Smoking and vaping compromise that. Once the virus gets down in your lungs you have this pro-inflammatory state that’s in your immune system and you can’t fight it off.”

There is a global movement to get cigarette companies to halt business in an effort to slow COVID-19’s impact on the world’s 1.3 billion smokers, in particular those in developing countries with overburdened health systems.

“The best thing the tobacco industry can do to fight COVID-19 is to immediately stop producing, marketing and selling tobacco,” Gan Quan, a public health specialist and a director at the International Union Against Tuberculosis and Lung Disease, said in a statement this month.

Even though he acknowledges people may be smoking more to help reduce stress and anxiety over the pandemic, Glantz said the bigger objective should be giving up habits that could potentially make you more susceptible to the infection.

The good news is that those who manage to quit smoking and vaping now will see almost immediate results. Cilia start to regenerate in three days, while normal function is typically returned within six months.

“If you stop using the products today, you’re improving your respiratory system tomorrow,” Glantz said.

Aidin Vaziri is a San Francisco Chronicle staff writer. Email: avaziri@sfchronicle.com Twitter: @MusicSF

Smoking and vaping FAQs People who smoke and vape may be at greater risk for serious complications from COVID-19, according to doctors and public health officials. Here is what you should know about correlation between vaping and smoking of tobacco or marijuana during the pandemic. Q. Are people who smoke or vape at higher risk of getting the coronavirus? A:Yes. Coronavirus attacks the lungs. Cigarettes and e-cigarettes compromise your immune system and lung function, while releasing ultrafine particles, industrial solvents and various irritants into your airway that disable the cilia, the small hair-like strands found in your lungs and respiratory tract that filter out toxins. Additionally, smoking and vaping require hand-to-mouth contact, which is one of the most common ways the disease is transmitted. Q. Are people who smoke more likely to develop serious complications from COVID-19? A:Yes. Smoking damages the cardiovascular system and reduces lung capacity, putting people at a higher risk of serious illnesses such as pneumonia, according to the World Health Organization. In a study from among Chinese patients diagnosed with COVID-19, researchers found the odds of disease progression — including to death — were 14 times higher among people with a history of smoking compared to those who did not smoke. Q: How long does it take to build up your defenses against coronavirus after quitting smoking? A: If you are considering quitting, now is the time to do it. Even though smoking and vaping have many significant long-term effects on your health, the benefits would be immediate. Cilia starts to regenerate in three days, while normal function is typically returned within six months. Q: How can I tell the difference between withdrawal and COVID-19 symptoms? A: Nicotine withdrawal symptoms typically include irritability and difficulty concentrating. Less common signs of withdrawal may include a cough or sore throat, symptoms that are commonly associated with COVID-19. But health officials say those should not cause concern unless your condition worsens. Q: What are some resources for quitting smoking? SmokeFree.gov 800-784-8669: American Lung Association 800-586-4872: National Cancer Institute 877-448-7848 Source: Chronicle research