Is vaping a health crisis?

An outbreak of severe lung illness related to vaping has affected more than 450 people and killed six in the United States in the past few weeks. The Centers for Disease Control and Prevention has advised people to avoid all e-cigarette products while it investigates. Symptoms for many of the victims quickly escalated from coughing and shortness of breath to a life-threatening condition known as acute respiratory distress syndrome.

The cause of the illness is unknown, but there's evidence to suggest it's connected to vaping THC, the psychoactive chemical in...