Facial hair and home oxygen therapy can prove a dangerously combustible combination, according to a Mayo Clinic report published in the peer-reviewed medical journal Mayo Clinic Proceedings.

To reach that conclusion, researchers reviewed home oxygen therapy-related burn cases and experimented with a mustachioed mannequin, a facial hair-free mannequin, nasal oxygen tubes and sparks. They found that facial hair raises the risk of home oxygen therapy-related burns, and encourage health care providers to counsel patients about the risk.

More than 1 million people in the United States use home oxygen therapy, and it is on the rise around the world, especially in countries where smoking is increasing, the researchers say.

Mustaches and other facial hair can act as kindling for nasal oxygen tubes when a spark joins the mix, even if the spark is just a tiny ember that flies at an oxygen tank user from a match, grill or fireworks.

“They can have very bad facial burns and airway burns also,” said senior author Andrew Greenlund, MD, PhD, a Mayo Clinic primary care physician. “When fire burns the airway, then you have swelling and tissue death. It can be very dangerous.”