The specific cause of the vaping-related illness sweeping across America, causing serious lung damage and the hospitalization of nearly 1,300 people so far, remains unknown.

According to the latest statistics issued by the Centers for Disease Control and Prevention (CDC), as of October 8, it has affected 1,299 people across 49 states, and 26 people have died in 21 states.

We know that the illness is likely related to THC-containing products for e-cigarette and vaping devices as most patients have reported using these before they got ill. However, no one product or substance relating to THC, the psychoactive component of cannabis, has been linked to all cases yet, and as such the specific chemical exposure causing the lung damage is still unknown.

Until now, the most prominent theory of the culprit was oils, like vitamin E acetate, used as an additive in vape liquid. It's thought that lipids, or fatty acids, inhaled from the oil are coating the lungs and causing cell death and pneumonia-like symptoms. Now a new study has revealed another symptom: lungs that look like they have chemical burns.

The study, carried out by researchers at the Mayo Clinic and published in the New England Journal of Medicine, took a pathological approach, reviewing the lung biopsies of 17 people who are clinically suspected of having the vaping illness, all of whom have a history of vaping, and 71 percent of whom report using THC-related products like marijuana and cannabis oils. Though it was a small group of subjects, all lungs showed acute injury, pneumonitis (inflammation of the lung tissue), and two later died. 

They all showed signs of chemical burns similar to those who have been exposed to toxic substances like mustard gas or chemical spills. Though the researchers don’t identify the kind of chemical that is causing the tissue damage, they suggest the vaping-related injuries are likely caused by the direct toxicity of inhaling noxious chemical fumes.

"While we can't discount the potential role of lipids, we have not seen anything to suggest this is a problem caused by lipid accumulation in the lungs,” said Dr Brandon Larsen, an expert in lung pathology, in a statement. “Instead, it seems to be some kind of direct chemical injury, similar to what one might see with exposures to toxic chemical fumes, poisonous gases, and toxic agents."

Because the subject group was small, the researchers acknowledge their study can only offer a "preliminary insight" into what may be happening, but they believe it will help doctors and clinicians struggling to diagnose vaping-associated lung injuries by offering a detailed review of the kind of damage that might be expected to be seen in lung biopsies going forward. Arming doctors and clinicians with as much information beforehand is vital, they say.

"This is a public health crisis, and a lot of people are working frantically around the clock to find out what the culprit or culprits could be – and what chemicals may be responsible," Dr Larsen said. "Based on what we have seen in our study, we suspect that most cases involve chemical contaminants, toxic byproducts or other noxious agents within vape liquids."

Until we know for sure for what is causing this illness, professional advice is to consider refraining from using e-cigarette or vaping products, especially non-regulated products like THC-containing liquids. If you think you have any of the symptoms reported – coughing, wheezing, shortness of breath, chest pain, nausea, fever, fatigue, and weight loss – see your health provider immediately.