Health officials in the northern US state of Wisconsin say eight teenagers are being treated in hospital for very seriously damaged lungs, and the youths from three counties seem to have only one similarity.

"We suspect that these injuries were caused by vaping," said Dr. Michael Gutzeit, chief medical officer at Children's Hospital of Wisconsin.  "The severity of health condition has varied, with some patients needing assistance in order to breathe."

All displayed symptoms in the weeks leading up to being admitted to hospital including cough, shortness of breath, fatigue, fever, anorexia, chest pain, nausea and diarrhea.  X-rays later revealed inflammation or swelling throughout both lungs.  The patients are responding to treatment but doctors are worried about the long-term consequences.  And since vaping has only been around for 15 years, long-term data doesn't exist.

In the place known as America's dairy state, 11 percent of middle schoolers have tried vaping products and 4 percent are regular users.  By the time they reach high school, those numbers shoot up to 32 percent and 20 percent respectively.

A health department study found that 80 percent of teen vapers started with flavored products, which come in kid-attracting varieties such as gummy bears, cotton candy, peanut butter cups, and cookies 'n cream.  But the US Centers for Disease Control and Prevention (CDC) say these flavors can often conceal a horribly harmful product, some of which have been found to contain heavy metals like nickel, tin, and lead.