This happens as your body works to protect your vital organs from the cold, said Dr. Suzanne Salamon, associate chief of clinical programs at Beth Israel Deaconess Medical Center in Boston.
"The blood vessels in all different parts of the body will constrict," she said. "They'll get smaller to try to preserve heat.
"What the body tries really hard to do is to protect the most important organs, which are the ones deep inside: the heart and brain and lungs," she said. "The body tries to keep those warm by redirecting heat from the fingers and toes inward, so the blood vessels in the fingers and toes get really small, and not enough blood goes through them."
Globally, more temperature-attributable deaths tend to be caused by cold than by heat, according to a 2015 study published in the journal The Lancet
A cold-hearted risk
Frosty weather can affect your heart, especially if you have cardiovascular disease
. "You always hear about people going out and shoveling snow and having a heart attack," Salamon said.
Cold weather can act as a vasoconstrictor, which means your blood vessels narrow, and that can play a role in raising the risk of heart attack, according to a 2014 Harvard Health Letter
published by Harvard Medical School.
"Snow shoveling is one example where we see people who have heart disease, or risk factors for heart disease, exerting themselves more than they may otherwise. Shoveling is hard work; people who have cardiac disease and back problems are at higher risk for injury or illness while shoveling," said Dr. Reed Caldwell, an assistant professor in the Ronald O. Perelman Department of Emergency Medicine at NYU Langone Medical Center and an emergency department physician.
A mere 1-degree Celsius reduction in temperature was associated with a cumulative 2% increased risk for heart attack, according to a 2010 study published in the British Medical Journal
The study involved data on 84,010 hospital admissions for heart attacks in England and Wales between 2003 and 2006. The researchers analyzed the data to determine any possible relationship between outdoor temperature and heart attack occurrences.
Some other studies have also found a correlation between the winter season and heart attacks and stroke, and the phenomenon has been sometimes referred to as "Merry Christmas Coronary
" and "Happy New Year Heart Attack."
However, the heart isn't the only part of the body that might be vulnerable to health problems in the winter.
Cold weather can wreak havoc on your lungs, as dry air may irritate the airways, especially for people with lung diseases such as asthma
, according to the American Lung Association
"Cold air causes bronchospasm, so people with asthma and COPD can find themselves having increased symptoms in the winter months," Caldwell said.
If you have asthma and are exposed to cold weather, "wear a scarf around your nose. That certainly helps, because then you're breathing in your own steam from your mouth," Salamon said.
On the other hand, a more well-known, cold-related health issue is frostbite.
Frostbite: A danger even for the eyes
Frostbite can occur in freezing temperatures when your blood vessels narrow, skin temperature drops and ice crystals form around and within your cells
, causing damage.
"There's a continuum of cold-related skin injury. The first is called 'frostnip,' and that is a cooling of the outermost skin tissue without any actual destruction to the tissue. You know this is happening because the skin can become discolored, sometimes bright red, and can look irritated and feel extra sensitive, and that's a good warning sign that the skin is getting too cold," Caldwell said.
"Then, frostbite involves actual skin destruction, and frostbitten skin usually appears pale, waxy, and can sometimes turn even purple or black as the tissue begins to die. Frostbitten skin can be numb or painless," he said.
Frostbite can even occur in your eyes, Salamon said. "When you're out in the cold windy weather, you can actually get frostbite of your eyes, which is really dangerous," Salamon said.
"The cold starts to form little blisters in your eye or little crystals on your skin, which can turn around and damage the skin or the eye itself," she said. "Those blood vessels really get very constricted, so there's not much blood going through it, which cuts down on the circulation of the eyes."
The blood vessels are constricting in order to prevent hypothermia
, a dangerous condition that occurs when your body loses more heat than it produces, causing the body's core temperature to drop below 95 degrees Fahrenheit.
"The most worrisome health effect from cold exposure is hypothermia, which can cause damage to vital organs, including the heart, nervous system and kidneys. In extreme cases, death can occur. This often is a result of abnormal cardiac rhythms," said Dr. Jeahan Colletti, an emergency medicine specialist at the Mayo Clinic in Rochester, Minnesota.
Those most at risk for hypothermia -- and any cold-related health hazard -- tend to be older adults, Salamon said.
"If people have a neighbor who is an older person, when there's weather that's really cold, they should check up on them. When people get really, really cold, they can get very confused and not even know enough to call for help," she said.
Tips to stay warm and healthy
What can people do to stay warm and healthy this winter? An important risk-reducing measure hinges on wardrobe.
"It's really important to dress in layers, so ... put on more than one pair of gloves and then a mitten on top of that, because the air that's trapped in between those layers help to keep you warm," Salamon said.
"Tight-fitting clothes are not a good thing, because you're not able to get the benefit of the layers. You really need to have looser sweaters, shawls if you're sitting inside, to try to layer up. It helps to have a ski mask to protect your ears and your nose," she said. "If you get wet, like if you're out playing in snow or shoveling snow, take off wet clothes, because the wet clothes really make it worse. They make things colder. ... Boots should be waterproof."
Preventive measures not only involve dressing for the cold but also avoiding too many cocktails in cold weather, said Colletti, the Mayo Clinic specialist.
"Avoid drinking alcohol when in the cold, as mental awareness is impaired, thereby limiting ability to recognize symptoms of significant cold exposure. Alcohol also causes dilatation of the body's blood vessels, increasing heat loss," she said.
Cold weather is also associated with weight gain, so another tip to stay warm and healthy this winter is to keep moving, said Dr. Luis Navarro, a physician and founder of the Vein Treatment Center in New York.
"Weight gain is common during the colder holiday months, and this can put our legs and circulatory system under more stress. Weight gain and colder temperatures could make varicose veins and spider veins worsen, due to the fact that blood is not efficiently pumping through the body," Navarro said.
"Even though it's cold, exercising and moving around helps to optimize circulation, which not only helps to keep our circulatory system healthy, but it can also help to keep us warm," he said. "Also, if you do experience leg pain as a result of restricted blood flow, I suggest elevating the legs for periods throughout the day so that they are raised above the heart. This helps maximize circulation."