Popcorn lung (bronchiolitis obliterans) is a type of lung disease, but it is not cancer. Although popcorn lung is very rare, some e-cigarette users may worry about it (and the media will tell you to worry about it).
A link between breathing in a chemical called diacetyl was made when a cluster of popcorn factory workers were all found to have the rare lung condition. It was not related to use of e-cigarettes. And more research is needed on the apparent link between diacetyl and popcorn lung. This includes the amount of the chemical at which any damage might occur.
A few studies, published around 2015, looked at whether e-cigarette liquids available at the time contained diacetyl. They found that a large proportion of e-liquid flavours tested did contain some level of diacetyl. The idea that e-cigarettes could cause popcorn lung came from these studies.
However, this study didn't look at whether there was a link between e-cigarette use and popcorn lung in people. So far, there's no good evidence that e-cigarettes could cause popcorn lung.
There's no good evidence that e-cigarettes could cause the lung condition called popcorn lung. There's been no cases of popcorn lung reported in people who use e-cigarettes.
Source: Cancer Research UK