There’s no way around it: The dangers of vaping are showing up everywhere—and now, the city of Milwaukee is urging its residents to immediately stop any use of vaping or e-cigarette devices.

On Wednesday, the City of Milwaukee Health Department (MHD) released a statement warning residents that 16 people had recently been hospitalized after developing chemical pneumonia (aka, chemical pneumonitis) as a result of vaping. According to the press release, all of the individuals reported using vape products or dabbing (vaping marijuana oils, extracts, or concentrates) in the weeks and months prior to hospitalization, though no specific products were identified.

“As someone who has worked diligently to eliminate access to tobacco and e-cigarettes among youth, I urge residents pay close attention to the poor health effects from using these products,” said Alderman Michael J. Murphy, co-chair of the City-County Heroin, Opioid, Cocaine Task Force said in the press release.

While vaping’s been in the news for various health problems lately, it hasn’t been tied directly to chemical pneumonia yet—so what exactly is it? Health spoke to pulmonologists (aka, lung doctors) to understand chemical pneumonia better. Here’s what they want you to know.

What is chemical pneumonia?

In the simplest terms, chemical pneumonia can develop after inhaling chemicals that cause your lungs to become inflamed. But here’s where it gets tricky: It’s hard to identify which chemical (or chemicals) are to blame for the irritation because a lot of different chemicals can be harmful. “Sometimes [it] can be hard to tell exactly what causes [chemical pneumonia]. The substances can vary from product to product,” Humberto Choi, MD, a pulmonologist at Cleveland Clinic, tells Health.

According to the US National Library of Medicine (NLM), some of the most common dangerous inhaled substances include chlorine gas, grain and fertilizer dust, fumes from pesticides, and smoke from house fires or wildfires.

Harmful chemicals get even trickier to pinpoint when vaping plays a role in chemical pneumonia. “The cases we are seeing in our nation—we do not know exactly what toxin is causing [them],” adds Melodi Pirzada, MD, chief of pediatric pulmonology at NYU Winthrop Hospital. That’s because, according to Dr Pirzada, we don’t know much about the additives in flavouring agents used in e-cigarettes.

She explains that symptoms of chemical pneumonia are similar to symptoms you equate with other forms of pneumonia: chest pain, cough, shortness of breath, and fever. According to the MHD’s press release, other symptoms they’re warning their residents about include fatigue, loss of appetite, nausea, and diarrhoea.

“Most diagnoses are made clinically, based on symptoms and findings in x-rays,” Dr Choi says. He adds that sometimes when patients simply avoid exposure to e-cigarettes after being diagnosed with chemical pneumonia, their symptoms improve. “That can be enough for someone to improve and for the lungs to heal,” Dr Choi says.

Other treatment methods include corticosteroids, per the NLM, to help reduce inflammation in the lungs. In more severe cases, oxygen therapy, which typically employs a ventilator, and a feeding tube may be needed. If left untreated, respiratory failure or death can occur, per the NLM.

You can prevent most cases of chemical pneumonia by only using household chemicals as directed and in well-ventilated areas, and always wearing breathing masks or limiting exposure to chemicals in workplace environments, according to the NLM. But when it comes to preventing chemical pneumonia from vaping, there’s a clear option: Stop vaping. Dr Choi sums up it up perfectly: “I usually tell people the lungs are made to breathe just clean air. When we’re inhaling any kind of chemical, that can trigger an inflammatory response.”

So, if you haven’t been convinced yet to put down the vape pen, maybe this news will do the trick.