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Is it safe to exercise when it's freezing cold outside?

With a winter chill gripping a large swath of the U.S. and some areas dipping below zero, runners, cyclists, skaters and other outdoor exercise enthusiasts need to plan ahead before they step out into frigid conditions, say health experts.

Icy weather can exacerbate asthma and kick up sinus issues; windburn can damage skin; hands and feet are especially vulnerable to frostbite; and as hard as it may be to believe when your teeth are chattering in a ski lift queue, even the sun can be a nemesis to winter fitness fans.

Wind chill and temperature tips

Why does that old winter wind feel so cruel when you're out on the slopes or embarking on a run or bike ride? Increased wind speed causes heat to leave the body more rapidly -- that's the wind chill effect.

Cycling enthusiasts are especially vulnerable to this wintry workout troublemaker, said Gloria Liu, associate editor at Bicycling magazine. They travel at speeds that actually create wind chill.

Liu told CBS News that the colder months might be a good time to swap out your racing bike for a mountain bike. "You'll be warmer at slower speeds, so mountain biking is a good winter riding option. The key is to stay warm while not overheating and sweating too much. Cold air plus moisture equals brrrr."

She opts for wearing layers and windproof clothing but warns that some can compromise breathability.

"If your clothes aren't breathable, you'll be a damp, sweaty mess in no time, which will ultimately make you even colder. That's why it's worthwhile to invest in a good, breathable windproof jacket, and it's why I prefer softshells over hardshell jackets -- they're more breathable," Liu said. She suggested wearing a good sweat-wicking base layer to help keep your core warm, as well.

If the temperature dips below 0 F (minus 17.8 C) or the wind chill is extreme, Mayo Clinic experts say consider taking a break or switching to an indoor workout instead.

The findings from one small 2014 study by Finnish researchers even suggest that exercising in the cold (32 degrees F) might lower the body's immune function, but the scientists didn't look at the long-term effects.

Keeping an eye out for asthma

There are many flavors of asthma, and some are impacted by cold weather, said Dr. David A. Beuther, associate professor of medicine and chief medical information officer at National Jewish Health in Denver, where they specialize in respiratory illnesses.

"For many asthmatics, extreme cold tends to be a trigger for them, particularly with exercise. It's more likely than not if you have asthma that cold air is a trigger for you. Some in that group don't have symptoms in any other circumstances," Beuther said.

"Experts argue over how it happens. One argument is that cold dry air dries out the airways and irritates them. There's another theory that it has to do with the temperature. It's not so much that cold air immediately causes problems, but when the airway rewarms itself during exercise, it causes the airways to swell," Beuther explained.

A brief 10 to 15 minute warm-up inside -- some calisthenics, jumping jacks, aggressive yoga, a fast walk or light jog on the treadmill -- to boost breathing and get your heart rate up a little can help prep the lungs before a workout outside, he advised.

One other simple technique is to simply breathe through your nose rather than your mouth while exercising in chilly weather. "Your nose is designed to humidify and warm the air that you breathe in. That's why it's narrow and has all these nooks and crannies," Beuther said. By the time it gets to your lungs, it's fully warmed.

Some with cold air-triggered asthma opt to step away from outdoor sports in winter, while others don't let it hold them back, but do have to make accommodations.

The recommendation for many is to use a rescue inhaler (such as albuterol) 15 minutes before exercise, he said. It may be highly effective in normal temperatures but not completely effective in colder environments when exercising, but he said, "It's still a good thing to do and the right thing to do" if a doctor recommends it. Check in with your doctor about whether or not a daily inhaled steroid medication is also needed, even if just during the winter sports season, he said.

Beuther said there are also non-medication strategies to reduce symptoms. Certain kinds of face masks and neck/mouth covers can reduce the amount of cold air in the lungs. They work like an old-fashioned scarf, but tend to get less icy on the outside and wet on the inside.

"You are looking for a balaclava or neck gaiter type design, often sold as a 'cold air mask' or 'cold air face mask,' but really it is a mask, typically fleece, with a heat and moisture exchanger for a mouthpiece," said Beuther. It's essentially like an artificial super-nose that conditions the air.

He said most masks do not rely on a power source, but instead trap heat and moisture from your exhaled breath and then impart it to the cold dry air when you breathe in.

Beuther and his colleagues have studied individually the effectiveness of a rescue inhaler and a face mask, and found that both were similarly effective at preventing the temporary decline in lung function due to cold-weather asthma.

Athletes should also check daily air quality, even in winter, he said. Cities near mountains, such as Denver, Los Angeles, and Salt Lake City, can act like a bowl where cold air settles in and then a warm layer settles on top of that and traps pollution that can irritate lungs more, Beuther said.

And if illness strikes, don't try to be a hero. "Colds and viruses are more prevalent and a big trigger for worsening asthma," he said. Reduce the intensity and duration of activity, or skip the workout, and check in with your doctor if symptoms persist. Particularly on a cold day, for people with cold-triggered asthma, he said, "more moderation is always a smart thing."

Avoid "skier's nose"

Ever been out for a run or sledding on a nippy winter day and your nose begins to run and you start to sneeze as if it's spring allergy season? You may be experiencing a common cold-induced rhinitis, or "skier's nose," said Beuther.

Symptoms hit when the lining of the nostrils produce an excess of a certain chemical when exposed to cold, dry air, he explained. It's a lot like a pollen or dust reaction, but the guilty party is the cold air.

Beuther said a face mask or scarf can reduce sneezing and sniffling, and over-the-counter allergy medications taken before outdoor winter activities can treat the symptoms. A pulmonary or allergy specialist can also prescribe a special nasal spray in more serious cases.

Be skin smart

Wear plenty of sunscreen when prepping for time outside, no matter how cold temperatures drop. Especially if you're skiing or participating in other high-altitude sports, said Dr. Darrell Rigel, professor of dermatology at New York University Medical Center and a member of the American Academy of Dermatology.

"People assume because it's the winter that you don't need as much protection from the sun," Rigel said, but the temperature on the thermometer doesn't tell you how strong UV rays are.

But nothing could be further from the truth, he told CBS News. "Extra altitude significantly increases the amount of ultraviolet radiation you get from the sun. In Colorado, at 8,000 to 10,000 feet, the UV intensity of the sun is stronger there than it would be in Miami Beach or the Caribbean at the same time of year."

Ultraviolet sun intensity increases eight to 10 percent for every thousand feet of elevation above sea level, he explained.

People often forget to put sunscreen under their chins when skiing, but Rigel said you can get sun exposure there from the reflecting snow. "A number of people get admitted to the hospital for sunburn after skiing," he said.

After applying a sunscreen, apply a moisturizer, too, Rigel recommends. "When it's really cold outside, having a good layer of moisturizer, besides putting a sunscreen on the cheeks and nose, keeps the heat in," he said.

A winter moisturizer rule of thumb: The greasier it is, generally the more affective it is. It puts a physical barrier on your skin and protects from windburn, the friction of the air on your skin, said Rigel.

Some products come in a sunscreen/moisturizer combo, but due to "chemistry problems," he said, it's hard to engineer those creams at high sun protection factors (SPFs). It's wiser to go with two separate products so that you can take advantage of a higher SPF, preferably 30 or up.

Cover fingers, toes, and head

Texas Heart Institute experts say when you're out in the cold, your body sends blood to its core, leaving hands and feet colder. They recommend wearing a thin pair of gloves under a heavier pair when exercising in the cold. Allow extra room in winter footwear for thermal socks or two pairs of regular socks.

Bicycling magazine's Liu said in addition to wearing gloves, cyclists should use shoe covers -- called "booties" in cycling slang -- and a beanie or hat that covers the ears.

Even a headband and keeping the neck warm are better than nothing. As much as 50 percent of your body's heat is lost through your head and neck.

When it comes to frostbite, the risk is less than five percent when the air temperature is above 5 degrees F (minus 15 C), but the risk increases as the wind chill dips. The Mayo Clinic warns that when the wind chill level drops below minus 18 F (minus 27 C), frostbite can occur on exposed skin in 30 minutes or less.

If you have other health conditions, check with your doctor before exercising on cold days to be sure it's safe. Some conditions can make you more vulnerable to cold weather health risks.

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