The heart has to do more work when you're exposed to really cold temperatures, whether outside or indoors. "Cold weather can increase your risk of a heart attack. When you’re outside in the cold, your heart works harder to keep you warm — leading to increased heart rate and blood pressure," Healthline wrote. The increased work rate can raise the risk of heart failure and expose underlying cardiovascular issues that, in normal temperatures, wouldn't be a problem. The exertion of exercise like shoveling snow is also a known trigger for heart problems and strokes.

Ever wondered why your fingers and toes are the first parts of your body to get cold when the weather is frightful? It's all part of the body's plan to protect its inner organs. That mission can result in some serious damage to the skin and tissues of extremities, otherwise known as frostbite.

During serious cold, explains the BBC, "the body is keeping its warm blood close to the centre, constricting blood supply in the outer regions such as the end of our limbs. In extreme cold, and especially if bare skin is open to the elements, this effect can end in frostbite. Blood flow is reduced, and the lack of warm blood can lead to tissue freezing and rupturing." Frostbite can occur within minutes of exposure to severe cold, and numb, white or yellowish skin that feels cold to the touch is a signal that there's not enough blood flow and you may be suffering permanent tissue damage.

Hypothermia is the technical term for a core body temperature that's less than 95°F. Researchers commented in 2015 that hypothermia occurs because of body heat loss: "In cold weather, the body can lose heat faster than it is produced, which uses up stored energy." It's also possible, they added, for people to get hypothermia in warmer temperatures if they're chilled for a long enough period. The risks of hypothermia include massive stress on your organs, particularly your heart, as they struggle to maintain enough warmth to function.

Symptoms of hypothermia can include intense shivering, a weak pulse and shallow breathing. At that point, raising your body temperature will probably bring you slowly back to normal, through blankets or heaters. However, there are more intense degrees of hypothermia, and those are more dangerous.

Hypothermia becomes more lethal the more time you spend outside. Shivering is, in fact, a positive sign. At a certain point in hypothermia, Chicago emergency medicine specialist Dr Jeff Schraider told NPR, "You'll stop shivering, and then your body temperature will start dropping at a more rapid rate." At that point, hypothermia accelerates and becomes more dangerous, as your internal metabolism — the mechanism that controls your energy levels and internal heat — begins to seriously slow down.

According to National Geographic, this is also the point where movement becomes more difficult, and your brain functioning slows down. "It's particularly dangerous if you have to make a crucial decision in the cold, like choosing a path on a hiking trail," they say. In this statement, hypothermic people become easily confused. It's not unknown for people with hypothermia to strip off all their clothes in the freezing weather, convinced that they're actually overheated. This is known as 'paradoxical undressing' and is very dangerous.

If you thought chilblains only belonged in 19th century novels, think again. They crop up in response to extreme cold, though less commonly than you think. The Mayo Clinic explains why: chilblains are "painful inflammation of small blood vessels in your skin that occur in response to repeated exposure to cold but not freezing air." You're more likely to get chilblains in extreme weather through sitting in an under-heated house or working in a chilly office than walking through sub-zero temperatures outside.

Chilblains most commonly turn up on extremities because of the restriction in blood flow. But they don't just have to do with cold. "If these chilly sections are then exposed to heat suddenly — perhaps you put your hands in front of a fire or heater — blood vessels near the surface become damaged and blood leaks out into surrounding tissue," wrote Claire O'Connell for the Irish Times. The resulting inflammation can attract infection and soreness. If you're in a cold house and your fingers are going numb, try to warm them up gradually rather than putting them close to something extremely hot.

The BBC noted that during the polar vortex, people in Chicago were being encouraged not to breathe deeply when they were outside in extremely cold air. Accuweather explains that extremely cold weather "causes airways to tighten" and also increases inflammation of the lung lining, which raises the risk of asthma attacks for people with sensitive respiratory systems. Even if you don't have asthma, breathing in extremely cold air isn't good for you. For people with chronic obstructive pulmonary disease, extreme cold air can prompt spasms in the lungs, impeding breathing. Cold, dry air raises your vulnerability for bronchitis if you exercise outdoors; there's even a condition known as 'runner's cough'.

If you'd like to get through extreme cold with as few health issues as possible, minimize your exposure to really cold temperatures outside. Wrap up warmly, particularly when it comes to your extremities, and pay attention to your health and that of those around you. If anybody is exhibiting confusion, shortness of breath or signs of frostbite or hypothermia, get them to a hospital ASAP.