Feeling cold all the time usually comes down to one of a handful of causes: your thyroid isn’t producing enough heat-generating hormones, your blood isn’t carrying enough oxygen, your body composition offers less insulation than average, or you’re not sleeping or eating well enough to fuel your internal furnace. Sometimes it’s a combination. The good news is that most causes are identifiable and treatable once you know where to look.
Your Thyroid Sets Your Internal Thermostat
The single most common medical explanation for constant coldness is an underactive thyroid, a condition called hypothyroidism. Your thyroid gland produces two hormones, T3 and T4, that tell your cells how much fuel to burn. T3 directly drives heat production, while T4 gets converted into T3 as needed. When levels of these hormones drop, your basal metabolic rate (the energy your body uses just to keep you alive at rest) falls with them. Your cells literally can’t generate enough warmth.
This isn’t just a mild chill. People with hypothyroidism often describe an inability to tolerate even small drops in temperature that don’t bother anyone else in the room. Other signs that point to your thyroid include unexplained weight gain, fatigue, dry skin, thinning hair, and constipation. A simple blood test measuring your thyroid-stimulating hormone (TSH) level can confirm or rule this out, and it’s the first thing most doctors check when a patient complains of chronic cold sensitivity.
Low Iron Starves Your Body of Heat
Iron-deficiency anemia is another major cause, and it’s especially common in women who menstruate, people who eat little red meat, and anyone with chronic blood loss from conditions like ulcers. The mechanism is straightforward: iron is essential for red blood cells to carry oxygen from your lungs to your tissues. When iron is low, oxygen delivery drops, and that disrupts two key warming processes at once. First, your body loses its ability to constrict blood vessels near the skin (a process that normally keeps heat trapped in your core). Second, your metabolic rate decreases because your cells don’t have enough oxygen to burn fuel efficiently. Less fuel burned means less heat produced.
If your cold sensitivity comes with unusual fatigue, pale skin, brittle nails, or shortness of breath during light activity, iron deficiency is worth investigating. A blood panel checking hemoglobin and ferritin (your iron storage protein) can identify the problem.
Vitamin B12 Deficiency Mimics Coldness
B12 plays a role in producing healthy red blood cells, so a deficiency creates a form of anemia similar to iron deficiency, with reduced oxygen delivery and less heat generation. But B12 adds another layer. When levels stay low long enough, the protective coating around your nerve fibers starts to break down, causing tingling, prickling, or numbness in your hands and feet. These nerve sensations are easy to misinterpret as feeling cold, even when the temperature around you is perfectly normal.
B12 deficiency is more common in people over 50 (who absorb less from food), vegans and vegetarians (since B12 comes primarily from animal products), and anyone taking long-term acid-reducing medications.
Body Fat Affects How Easily You Chill
Body composition has a surprisingly large influence on how cold you feel. Research published in the Proceedings of the National Academy of Sciences found that both basal heat production and insulation from body fat are the two biggest factors determining the temperature at which your body starts working harder to stay warm. People with lower body fat percentages had to vasoconstrict more aggressively in mild cold and showed higher muscle electrical activity (essentially, early shivering) compared to people with more body fat. Their core temperature also dropped more readily as the room got cooler.
This means that if you’re lean, especially if you’re also small-framed, your body simply has less insulation and produces less baseline heat per unit of surface area. It’s not a medical problem in itself, but it explains why two people in the same room can have completely different experiences of the temperature. The study also found that when both metabolic rate and insulation were accounted for, sex alone didn’t significantly predict cold tolerance. In other words, the reason women tend to feel colder than men has more to do with body size and composition than with being female.
Poor Sleep Makes You Feel Colder
Sleep and temperature regulation are controlled by the same neurons in the brain. Research from Washington University in St. Louis confirmed what many people notice firsthand: losing sleep makes you feel colder. The connection isn’t just psychological. When your sleep is disrupted or chronically insufficient, the brain circuits that manage your internal thermostat don’t function properly. The researchers found that sleep loss shifts temperature preference toward wanting more warmth, a biological signal that your body’s heat regulation is compromised.
If you’re consistently getting fewer than seven hours, or your sleep is fragmented by stress, noise, or a sleep disorder, that alone could explain why you’re reaching for an extra blanket more often than the people around you.
Circulation Problems and Raynaud’s
If your cold sensitivity is concentrated in your fingers and toes rather than your whole body, circulation may be the issue. Raynaud’s phenomenon causes the small blood vessels supplying your skin to overreact to cold or stress, clamping down far more than necessary. During an episode, the affected fingers or toes first turn pale as blood flow drops, then may shift to a bluish color. They feel numb and cold. When blood flow returns, the skin changes color again and you may feel throbbing, tingling, or swelling.
Primary Raynaud’s (the more common type) happens on its own without an underlying disease and is more of a nuisance than a danger. Secondary Raynaud’s is linked to autoimmune conditions and tends to be more severe. If your fingers or toes regularly go white or blue in response to cold that doesn’t bother other people, it’s worth mentioning to your doctor, particularly if episodes are painful or one-sided.
Medications That Cool You Down
Certain medications cause cold hands and feet as a direct side effect. Beta blockers are the most well-known culprit. Non-selective beta blockers like propranolol block stress hormones not just in the heart but throughout the body, which can narrow blood vessels in the extremities and reduce blood flow to the hands and feet. This effect is more pronounced in older adults. If you started feeling persistently cold around the same time you began a new medication, that timing is worth noting and discussing with whoever prescribed it.
Dehydration and Undereating
Your body needs both water and calories to maintain its temperature. When you’re dehydrated, your blood volume drops, which means less warm blood circulating to your extremities. Severe dehydration can cause dangerously low blood volume, but even mild, chronic underhydration can leave you feeling chillier than usual.
Similarly, if you’re eating significantly fewer calories than your body needs (whether from intentional dieting, stress, or disordered eating), your metabolic rate slows to conserve energy. One of the first things your body sacrifices is heat production. Chronic dieters and people with eating disorders frequently report feeling cold, and it’s a direct consequence of the body downshifting its metabolism to match reduced fuel intake.
Patterns Worth Paying Attention To
Normal body temperature varies more than most people realize. The old 98.6°F standard is an average, but healthy individuals can range from 97°F to 99°F, and everyone runs cooler in the early morning than later in the day. Some people simply run on the lower end of normal and feel cold more easily without anything being wrong.
The signals that suggest something medical is going on include cold sensitivity that’s new or worsening, cold intolerance paired with fatigue or unexplained weight changes, numbness or color changes in fingers and toes, hair thinning or dry skin alongside the coldness, or feeling cold even in warm environments where others are comfortable. Any of these combinations points toward a cause worth identifying, and most can be detected with basic blood work.