The caution has taken on new urgency in recent months as authorities scramble to understand a rash of mysterious vaping-linked illnesses that have put healthy people in the hospital with serious lung diseases. The latest federal data show there are more than 2,000 cases across every state but Alaska connected to vaping or e-cigarettes, which are battery-powered devices that can look like flash drives and pens and that mimic smoking by heating liquids containing substances such as nicotine and marijuana. At least 39 deaths in 24 states and the District of Columbia have been confirmed, the Centers for Disease Control and Prevention says.

On Friday, CDC officials announced a “breakthrough” discovery, saying they identified vitamin E acetate in the lung fluids of 29 people sickened in the outbreak of dangerous vaping-related lung injuries. The finding points to the oil as a likely culprit in the outbreak, a top official said.