How Cold Is Too Cold to Run Outside?

Dedicated runners and winter athletes will tell you: exercising in the cold isn’t as difficult as it seems. Personally, I prefer to risk frostbite during any treadmill run that lasts more than 20 minutes. But is there a point where winter racing goes from difficult to dangerous?

There is no clear limit

Most experts suggest the danger zone begins around -18°F (-28° Celsius), especially when taking wind chill into account. At these extreme temperatures, the risk of frostbite increases significantly and breathing freezing air can become uncomfortable and even harmful to your lungs and airways.

But beyond the raw temperature, certain conditions should encourage you to favor the treadmill rather than the trail. Wind chill is much more important 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 quickly accelerates heat loss.

Icy conditions create obvious fall hazards, and a twisted ankle or other injury becomes much more serious when you’re miles from home in subzero temperatures. If footing is dangerous on ice or you are unable to adequately protect your extremities with the equipment you have, it is wise to avoid outdoor running. Trust your instincts: If the cold is really painful in the first few minutes rather than just uncomfortable, your body is sending a clear message.

Again, this threshold is not absolute. Your personal cold tolerance, experience level, equipment you own, and specific weather conditions all play a role. I know I managed to run in 10°F, mainly because it was very sunny, windless, and I was perfectly bundled up. Here are some activities to do if you’re a brave soul heading out for a run in the freezing cold.

If you are venturing out into very cold weather, preparation is essential. Dress in layers using moisture-wicking base layers, insulating mid layers, and windproof outer shells. Carefully protect your extremities with gloves or mittens, a hat or headband, and warm socks. A neck gaiter is essential 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 have it on your back when you sweat and are more vulnerable to heat loss on the return journey. Reduce your shopping and stay close to home or in areas with rescue options. Let someone know your route and expected return time. This also allows you to physically change your route to accommodate layers. Plan a race where you can shed extra layers after the first mile, then gain them back on the way back.

Pay attention to your body throughout the race. Any numbness, excessive pain, confusion, or severe shaking means it’s time to go inside immediately. Remember, you can always cut a run short: there’s no shame in prioritizing your safety over a workout.

Another tip, from many personal experiences: pay close attention to mouth breathing when running in cold, dry air. I recommend running with cough drops to help you practice breathing through your nose.

The essentials

I always tell myself that if something goes wrong after my first mile, I have the right to turn around and walk home. Allow yourself extra indulgence in extreme weather conditions. If you really can’t stand missing miles, consider a hybrid plan of doing half your route outside and the other half on a treadmill.

You can run outside in fairly cool temperatures before seriously risking frostbite or any other consequences of the cold. For most runners, the practical limit for safe outdoor running is between 0 and -20°F. As long as you are prepared with protective gear, you can listen to your body to acclimate to cold temperatures as best as you personally can.