Dedicated runners and winter athletes will tell you that exercising in the cold is not as tough as it looks. Personally, I’d rather risk frostbite over any treadmill run that lasts longer than 20 minutes. But is there a point where winter runs cross over from difficult to dangerous?
There is no clear cut-off
Most experts suggest that the danger zone begins around -18°F (-28° Celcius), particularly when factoring in wind chill. At these extreme temperatures, the risk of frostbite increases dramatically, and breathing frigid air can become uncomfortable or even harmful to your lungs and airways.
But beyond the raw temperature, certain conditions should prompt you to choose the treadmill over the trail. Wind chill matters significantly more than the actual temperature—a 20°F day with 25 mph winds feels like -4°F and carries similar risks. Precipitation combined with cold is particularly dangerous, as wet clothing rapidly accelerates heat loss.
Icy conditions create obvious fall risks, and a twisted ankle or other injury becomes far more serious when you’re miles from home in subzero temperatures. If the footing is treacherous with ice or you’re unable to adequately protect your extremities with the gear you have available, it’s wise to skip the outdoor run. Trust your instincts: If the cold feels genuinely painful within the first few minutes rather than just uncomfortable, that’s your body sending a clear message.
Again, this threshold isn’t absolute. Your personal cold tolerance, experience level, the gear you own, and specific weather conditions all play a role. I know I’ve managed runs in 10°F, mostly because it was plenty sunny, with no wind, and I was expertly bundled up. Here are some of things to do if you’re a brave soul heading out to run in the freezing cold.
If you do venture out in very cold weather, preparation is everything. Dress in layers using moisture-wicking base layers, insulating middle layers, and windproof outer shells. Protect your extremities carefully with gloves or mittens, a hat or headband, and warm socks. A neck gaiter is a must-have to pull up over your nose and mouth to help warm the air before it reaches the lungs.
Start your run into the wind so you’ll have it at your back when you’re sweaty and more vulnerable to heat loss on the return trip. Keep your runs shorter and stay close to home or in areas with bailout options. Let someone know your route and expected return time. It also helps to physically modify your route to accommodate layers. Plan a run where you can shed extra layers after the first mile and then pick them up on your way back.
What do you think so far?
Pay attention to your body throughout the run. Any numbness, excessive pain, confusion, or severe shivering means it’s time to get indoors immediately. Remember that you can always cut a run short—there’s no shame in prioritizing your safety over a workout.
Another tip, from plenty of personal experience: Be extra aware of mouth-breathing while running in cold, dry air. I recommend running with cough drops in order to help you practice breathing through your nose.
The bottom line
I always tell myself that if something feels off after my first mile, I’m allowed to turn around and walk home. Grant yourself extra leniency in extreme weather conditions. If you really can’t bear missing any miles, consider a hybrid plan of running half of your route outdoors and half on a treadmill.
You can run outside at quite chilly temperatures before you seriously risk frostbite or any other cold-weather consequences. For most runners, the practical limit for safe outdoor running falls somewhere between 0 and -20°F. As long as you’re prepared with protective gear, you can listen to your body to acclimate to cold temperatures as best as you personally can.
