We, along with other mammals and birds, are endothermic. We use thermoregulation to maintain a constant internal body temperature, between 37 and 37.5 ºC. When the external environment changes, “a series of physiological responses are initiated, including lowering the temperature of the tissues—skin, blood, and muscles,” says Dr. Joseph Costello, an exercise and environmental physiologist at the labs of extreme environments from the University of Portsmouth. “If the exposure is for a longer period of time, you may also see a reduction in core body temperature.”
Thermoregulation is controlled by the hypothalamus, a structure deep in the brain that maintains internal balance – or homeostasis – by regulating processes such as heart rate and body temperature. If the hypothalamus senses that the body is getting cold, it sends signals to the skin, glands, muscles and organs, initiating responses that will keep the body warm and protect vital organs.
When the body gets cold, protecting the internal organs is the first priority. If the ambient temperature drops to 15ºC, the blood vessels close to the skin constrict. Blood flow is redirected from the extremities (hands, feet, arms, legs and outer skin) to the core to keep the organs warm and protected. The perception of cold begins with the skin. Some people can feel the cold more than others, particularly women, the elderly and young children. Women have more body fat than men. A thick layer of subcutaneous fat insulates internal organs but blocks the flow of warm blood to the skin and extremities. They also typically have less muscle to generate heat through shivering. Having less muscle also lowers your basal metabolic rate, the ability to burn energy from food.
A cold body redirects blood from the extremities to the vital organs. Photography: Alamy
In older people, the body has a harder time pumping blood to the places that need it, as the metabolic rate decreases with age. Meanwhile, babies, says neonatologist Dr Chris Dewhurst, of Liverpool Women’s NHS Foundation Trust, have underdeveloped metabolic mechanisms to respond to heat stress. “For example, babies can’t shake,” she says. “They also have a high body surface-to-mass ratio, which means they’re more likely to catch a cold.” Babies, however, have brown fat, the same type of fat that hibernating animals have. “Brown fat generates heat by using calories,” says Dewhurst. “The calories that would normally be used to grow muscle and brain tissue.”
Using calories to stay warm, he warns, affects brain growth and development. When body temperature drops, blood pressure rises as more blood than usual is pumped through a smaller space. In an attempt to reduce fluid volume and lower blood pressure, the kidneys respond by filtering excess fluid from the blood, so you can urinate more often. This is called cold diuresis. The lack of blood in the skin can result in a bluish tint as the skin drops to the surrounding temperatures. When the body is exposed to cold for long periods, this protective strategy can reduce blood flow in some areas of the body to dangerously low levels.
Central temperature
At this point, the body has made the decision to risk sacrificing the most expendable parts (fingers, feet, ears, nose, cheeks) to preserve the core temperature. When the skin drops to -2ºC, body tissue begins to freeze. As the skin freezes, it begins to feel waxy, tingly, or itchy, and then feels numb. The deeper tissues then freeze. This is a freeze. The skin may turn blue, gray or black. At -4ºC, ice crystals can form in the blood. In deep freezes, the skin may feel hard, like wood. Muscles and bones begin to freeze.
When the body can no longer maintain core temperature by constricting blood vessels, it shivers to increase heat production. Skeletal muscles contract to generate heat. This is the first symptom of hypothermia, which affects all body systems: metabolic rate, mental awareness, nerve conduction and neuromuscular reaction time, as well as the cardiovascular and respiratory systems. As body temperature drops, slurred speech, lack of coordination, and memory loss develop. When the core body temperature drops to 32 ºC, the shivering stops. When the core temperature drops below 30ºC, the heart beats irregularly. Kidney function fails. Fluid builds up in the tissues and air spaces of the lungs. At 29ºC there can be loss of consciousness and, at 26ºC, death.
Perpetually cold
What if you’re only mildly cold but for a long period of time, for example, you can’t heat your house? “If exposed to less intense cold for extended periods of time, people can develop non-freezing cold injury,” says Costello’s colleague and environmental physiologist Dr Clare Eglin. “Symptoms of non-freezing cold injuries include impaired sensory function, sensitivity to cold, and pain as a result of damage to blood vessels and nerves in the hands or feet. If severe, these symptoms can last for many months.” .
Cold air can irritate the respiratory tract. Photography: Alamy
Are you more likely to catch a cold when you’re cold?
Breathing cold air for an extended period of time can also irritate the airways and lungs, even in healthy people, and can worsen existing breathing problems such as asthma, bronchitis or chronic obstructive pulmonary disease. When inhaled, the nose and mouth usually warm and humidify the air before it reaches the lungs. When the air is cold, the upper airways react by narrowing, making it difficult to breathe. Also, cold air contains less moisture than warm air, so breathing it can dry out the airways. “Respiratory infections thrive in colder temperatures,” says Erika Radford, head of health advice at Asthma + Lung UK. “Winter is already a deadly time for people with lung conditions and the last thing we want to see is more people being rushed to hospital struggling to breathe, due to exposure to the cold.”
We are in uncharted territory. Homes that weren’t cold before will be cold for the first time, UCL Senior Research Associate Dr Tammy Boyce
keep warm
There are some scientifically proven ways to stay warm, and some old wives’ tales to avoid.
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Wear a hat: Scientists have discovered that we lose more heat from our bodies than from our heads. However, it’s still worth wearing a hat because if your body is hot but your head is cold, you won’t be shivering. This causes the core temperature to drop rapidly.
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Layers of wear: Wearing many thin layers to trap air reproduces the horror effect – better known as goosebumps – that many animals benefit from, where air is trapped between the hairs that have been made stand on tiptoe by the contraction of small muscles known. as pili guide at the base of each hair follicle.
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Get active: Physical activity causes muscles to contract, break down more nutrients, which generates heat. In fact, just walking up and down a step can produce an additional 200 watts of heat and raise your body temperature quickly. But don’t overdo it: If you get hot and start to sweat, the evaporation of sweat can cause rapid heat loss.
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Don’t drink alcohol: This sends blood to the surface of the skin but away from the core, so the body temperature drops profoundly, increasing the risk of hypothermia. Alcohol has also been found to inhibit the natural shivering response as well as the perception of cold.
Houses in Ruskin Park, south London, during the March 2018 cold snap known as the Beast from the East. Photograph: Richard Baker/In Pictures/Getty Images
Fuel poverty
According to University College London (UCL) experts, this winter thousands of people will die and millions of children will suffer due to “epidemic levels” of energy poverty. “We are in uncharted territory,” says Dr Tammy Boyce, senior research associate at UCL and co-author of the Marmot review. “Homes that were not cold before will do so for the first time. People who have never known energy poverty will be fuel poor.” People with disabilities, the elderly and children will be hardest hit, he adds, and that affects everything including school performance and mental health, as well as physical well-being. “The only good thing about this,” says Boyce, “is that people realize the impact housing has on health.”