The extreme cold weather and the threat of power outages may have folks turning to space heaters or alternative forms of heat. But that can carry a risk that can cause severe sickness and even death.

The danger is carbon monoxide, or CO — a colorless, odorless gas.

“It’s called the ‘silent killer,’ mostly because it is somewhat insidious,” said Dr. Chloe McCoy, an emergency room physician with MedStar Health. “A lot of the symptoms are nonspecific and may feel like flu-like symptoms.”

Using space heaters, gas furnaces, fireplaces and portable generators that don’t have proper ventilation can put CO into your home.

Advanced cases can leave someone feeling confused and disoriented, and it can even cause them to pass out. If you start feeling symptoms like that, and you’re using a generator or alterative heat source, turn it off if possible.

Then, McCoy said, “You need to get out of the house.”

“Getting exposed to fresh air is the first priority, and then the second priority is to call 911 and have emergency services address the issue,” she said.