After using a marijuana vape pen for just six months, a 49-year-old retired dog trainer went to the doctor coughing and wheezing, reporting shortness of breath upon exertion. The woman had smoked off and on through her teens and twenties, but was healthy — other than her worrying throat symptoms.

Her doctors gave her a rare and surprising diagnosis: hard-metal pneumoconiosis — a lung disease known as “cobalt lung.”

Until now, this lung condition was most often seen in one particular group of people: metal workers. Typically, people who sharpen tools, polish diamonds, or make dental prosthetics are at risk of developing “cobalt lung,” not dog trainers.

So what caused the woman’s lung condition? Worryingly, it was probably her marijuana vape pen.

That’s the conclusion of a case study on the woman, published this week in the European Respiratory Journal.

Researchers analyzed the vape liquid from her “ZenPen,” finding toxic metals in the juice like nickel, aluminum, lead, and, you guessed it, cobalt. They also have a theory for how those metals might make their way from the vape into the woman’s airways in the first place — it may be to do with the way marijuana vape pens work.

“Exposure to cobalt dust is extremely rare outside of a few specific industries,” Rupal Shah, paper co-author and researcher at the University of California, San Francisco said in a statement.

“This is the first known case of a metal-induced toxicity in the lung that has followed from vaping and it has resulted in long-term, probably permanent, scarring of the patient’s lungs.”

What is cobalt lung?

Cobalt lung is a doctor’s worst nightmare. The condition is irreversible and can cause lifetime pulmonary problems.

The condition is diagnosed by examining lung tissue under a microscope, Kirk Jones, co-author of the case history and researcher at UCSF, said.

“It has a distinctive and unusual appearance that is not observed in other diseases,” he said.

Pictures of the patient's lung scarring as seen under a microscope. Giant cell interstitial pneumonia secondary to cobalt exposure from e-cigarette use

When someone breathes in vapor containing heavy metals, the fine particles can lodge in their lung cells, causing irreparable damage. The damaged cells become “cannibals,” engulf other cells, and eventually form giant white blood cells that can be seen clearly under a microscope. These huge “macrophages” can lead to permanent scarring, breathing problems and chronic coughing.

The scarring can’t be cured — it can only be minimally improved if the person stops exposing themselves to hard metals, or takes steroids. In the dog trainer’s case, she stopped smoking and vaping immediately upon diagnosis. She tried various medications and a steroid, which slightly improved the scarring and her other symptoms. But the condition itself persisted.

The relative risk of developing this devastating condition is low for most vape users, Shah said. But that doesn’t mean it should be treated lightly.

“But the problem is that the inflammation caused by hard metal would not be apparent to people using e-cigarettes until the scarring has become irreversible, as it did with this patient.”

Basically, you wouldn’t know you had the condition until it was too late.

Coil culprit

The trainer’s heavy-metal exposure likely came from the heated coil of her vape pen, the researchers suggest. A 2018 study suggests that hard metals are likely leaching from the heated coils in vape pens, not the refill cartridges of vape juice. There’s also a growing body of evidence that e-cigarettes contain toxic and potentially cancer-causing metals. Other studies suggest that the metal levels in e-cigs are similar to those found in cigarettes, and sometimes much higher.

Marijuana pens may be especially dangerous, as they typically heat vape liquid about 230 degrees Celsius, while nicotine vapes heat liquid to 110 to 185 degrees C — the higher temperatures could exacerbate metal leaching.

Stop replacing cigarettes with e-cigs

E-cigs may be presented as a “lesser of two evils” alternative to cigarettes. But vaping isn’t harmless, and, as this case study shows, the consequences can be devastating.

“People who vape are often looking for a safer alternative to smoking,” Jones said. “But as lung physicians, it is our job to be concerned about the substances that are inhaled into the lung, particularly those substances that can bypass our usual defense mechanisms such as these ultra-fine mists.”

The vaping-cobalt lung connection is troubling news for the vape industry, which has been plagued by recent reports on harmful health risks of the practice.

This is just the beginning, the researchers suggest.

“We believe it is likely not just that this will happen again, but that it has happened already but not been recognized,” Jones said.

The middle-aged dog trainer may live out her days with breathing problems and lung damage, after just six months of using a marijuana vape pen.

The hope is that other people won’t have to do the same.

Editor’s note: Thanks to a reader for pointing out that a previous version of this article did not make clear that the case study’s finding directly applies only to a marijuana vape pen. Inverse regrets the error.