There's a popular perception, particularly among new runners, that running in cold weather is bad for you. Not so. Unless the temperature is so low that you seriously risk frostbite, it's warm enough to run. Even in those frostbite-threatening lows, carefully chosen clothing can protect you well enough to allow your daily jaunt.
No, Your Lungs Won't Freeze
Your body does a great job of heating the air that you breathe. There's no danger of freezing either your lungs or your windpipe. You may feel a little bit of a "burning" feeling in your throat or chest if the air is very cold, particularly if you are not yet in tip-top shape. If this is the case and you find it uncomfortable, covering your mouth with a scarf or ski mask can help heat up the air a bit more.
Do be aware, though, that cold air can aggravate an existing infection in your chest or throat. If you have a chest cold or a sore throat, take a break from running outside, or you risk making things worse. If you have a head cold, on the other hand, the adrenaline your body pumps out while running can actually help clear up your stuffiness. As always, use good judgment. If you are very sick, you have no business running. Take care of yourself, and get some rest before heading back out on the roads.
Dressing the Part
The key to cold-weather running is dressing in layers, which helps trap warm air near your body for the best possible insulation. The stuff those layers are made of is very important. In general, avoid cotton; it holds moisture and will eventually start to chill you. For details on some of the high-tech fabrics that breathe, wick moisture, or resist wind and water, check out our survey of running fabrics ("The Well-Dressed Runner"). Meantime, here are some details on how best to layer your running clothes.
The layer closest to the skin should be a tight, lightweight fabric that "wicks" water away from the skin, keeping you dry. Shirts should be long-sleeved and skin-tight (without chafing). It is very important to avoid wearing cotton as your inner layer.
The next layer should be a looser, medium-weight fabric -- preferably one that wicks water. A zipper at the neck is convenient for temperature control. On the legs, a layer of Lycra tights or some fleece pants will do the trick.
This final layer is really necessary only when it is bitterly cold or very windy. The shell should be resistant to both wind and water and preferably made of a fabric that "breathes" and allows moisture to escape. As with the outer layer, it's helpful if the shell has a zipper to allow for temperature control. The shell can be an entire suit, or just a jacket or pair of pants.
Just like mom always said, you lose a lot of heat from your head, and it's important to keep it covered. A wicking fabric is ideal, but cotton will do if you must. You might also consider wearing a balaclava, an item you pull over your head and neck, with a hole for your face. Here, too, a wicking fabric is best.
Cheap cotton gardening gloves from your local hardware store will do the trick, but a wicking fabric will keep your hands warmer and drier.
A wicking sock will seem less heavy and your feet will be drier than a conventional cotton sock. Don't kill yourself on this point, though. As long as you don't get your feet wet, they'll stay pretty warm, even with cotton socks.