Most runners want to know when it is too cold to run outside. There are no clear-cut rules under which all experts agree. It is ultimately the runner’s personal tolerance and comfort level.

Runners with conditions such as asthma, cardiovascular disease, diabetes, Raynaud’s syndrome and low body fat may be particularly sensitive to running in cold weather.

Some runners find they can only handle running in temperatures just below freezing (32° F), but not below that. If they do run in lower temperatures, they have difficulty breathing or experience numbness in their fingers and toes.

Other runners find that if they are dressed suitably, they can reasonably handle running at any temperature, no matter how far below freezing the weather is.

However, the American College of Sports Medicine recommends runners exercise caution when deciding to run outside when the air temperature falls below -18° F because tissue injury can occur in 30 minutes or fewer under these conditions.

It is also important to be aware of the wind chill factor, as even seemingly mild winds can have a significant effect on lowering the temperature on a cold day. For instance, when the air temperature is 30° F and the wind speed is 10 mph, the resultant conditions will behave as if it was actually 21° F.

Most weather apps will state the current wind chill factor for an exact location.

Risks of Running in the Cold

Frostbite is a direct freezing injury of body tissue that occurs with exposure to extreme cold. The nose, ears, fingers and toes are particularly prone to frostbite. Runners who notice the early signs of frostbite, including cold, red skin (which will progress to a tingling, numbness or a burning sensation) should immediately seek shelter to rewarm the skin.

Hypothermia, which is a drop in core body temperature to below 95° F, occurs when the total loss of body heat exceeds your physiological heat production. There are three grades of hypothermia and, unfortunately, severe hypothermia can be fatal. Shivering is an early warning sign of hypothermia, but shivering ceases as the condition becomes increasingly dire. 

Breathing can also be a challenge in the cold, with many runners experiencing a burning sensation in the throat or lungs. This can be especially problematic for runners with asthma.

Precipitation, which can include snow, sleet or freezing rain can make an outdoor run dangerously slippery. Icy conditions are particularly difficult. During these occasions, running indoors on a treadmill or other indoor options should be considered.

Underfoot conditions, even when roads have been plowed, the shoulders and sidewalks are often still covered in snow, slush and ice, adding to your running risks. Falling while running can result in an injury that could take you out of the game for some time. It is always best to err on the side of caution when road conditions are questionable. Some runners use ice spikes or products such as Yaktrax which increase the traction of running shoes on slippery surfaces.

Darkness is often the running time of choice due to the short daylight hours. Always ensure your path is well illuminated with a headlamp or nearby lighting, if available. Wear reflective clothing so that you are visible to drivers who might not otherwise see you.

Tips for cold weather running

Warm up indoors first. Sip a warm drink and conduct your warm-up routine indoors so that you feel ready and warm before heading out into the frigid air. This can also prevent pulling a cold muscle and make the blast of winter air a little more refreshing as opposed to heading out without the warm-up phase of your run.

Dress properly. Your clothing can make all the difference in your ability to run in the cold. Wear synthetic or wool-base layers and windproof outer layers. Avoid cotton. Overdressing can lead you to be overly hot and sweaty when running. Once you’re damp, you will end up feeling colder. Using layers is ideal since they trap heat and can be removed if you are feeling too warm. It is also important to wear warm socks, gloves, a hat and a gaiter to avoid exposing as much skin as possible.

Alter your route. Run small loops close to home or several short out-and-back routes. This will allow you to easily head back inside if you feel too cold or start noticing signs of hypothermia or frostbite.

Modify your mindset. Rather than focusing on your performance, focus on safety. At the first signs of harmful symptoms, think safety and head back inside. Be satisfied with what you were able to do under the circumstances.

Hydrate with warm liquids. During and after your run, drink warm (not hot) water or tea to make sure your core temperature remains at the proper level.

Shower in warm water as soon as you get home. Be careful not to adjust the temperature of the water too hot, as your perception of hot and cold may be distorted due to your limbs being cold or numb.

Finally, before heading outside in the extreme cold, ask yourself if you have safer options such as a treadmill or cross-training at a nearby gym. Weigh the options and consider what you really gain by running outside.