South Korea is the latest country to warn of risks from vaping.
On Wednesday officials advised people to stop using liquid e-cigarettes and said the country is weighing a sales ban.
That would hit major producers like Juul.
South Korea is the world's second-biggest market for heated vape products after Japan.
The country's Health Minister says they'll speed up studies to work out if there's scientific basis for a ban.
(SOUNDBITE) (Korean) SOUTH KOREA'S HEALTH MINISTER, PARK NEUNG-HOO, SAYING:
"The situation as it stands is considered a grave threat to public health, as suspected cases of lung damage have been reported domestically, after cases overseas of lung damage and death."
U.S. officials have reported 33 deaths from a mysterious respiratory illness linked to vaping.
South Korean health officials say a local case of pneumonia in a 30-year-old who vaped was reported this month.
Countries around the world have been pulling e-cigarette products from shelves as vaping faces rising scrutiny.
U.S. e-cigarette maker Juul Labs began selling their devices in South Korea in May.
After South Korea's comments on Wednesday, Juul Labs' local office said in a statement their products had no harmful substances.