Have you heard of popcorn worker lung? Over the past few decades, several workers at popcorn plants developed a lung disease that permanently scars the airway. The damage is so bad that some of the popcorn workers need lung transplants.
Scientists think the disease occurs as a result of breathing in a chemical used to create an artificial butter taste called diacetyl. Lab rats that breathed lots of the stuff ended up with the same kind of lung damage.
Since you aren't a lab rat, and most likely don't work at a popcorn factory, you're okay right?
Well, probably, though a man in Denver showed up in a doctor's office with telltale symptoms. It turns out he'd been making at least one bag of butter-flavored microwave popcorn a day for ten years, and when he opened a bag, he'd take a deep whiff of the buttery scent. In doing this, he was breathing in a lot of diacetyl, affecting the man just like the popcorn factory employees.