Feeling cold all the time usually signals that your body isn’t producing or distributing heat efficiently. The most common culprits are an underactive thyroid, low iron levels, poor circulation, or simply not having enough body fat to retain warmth. Less often, the issue is nutritional, hormonal, or stress-related. If you’re also wondering why you keep catching colds (the illness), that’s a different but related question, and we’ll cover that too.
Your Thyroid Sets the Thermostat
The single most common medical reason people feel persistently cold is an underactive thyroid, a condition called hypothyroidism. Thyroid hormones control your basal metabolic rate, which is essentially how much energy your body burns at rest. When thyroid hormone levels drop, your cells produce less heat in several ways at once: they make less of the energy molecule ATP, they run fewer of the internal “engines” in your muscles that generate warmth as a byproduct, and they become more efficient at conserving energy rather than releasing it as heat.
Your thyroid also governs brown fat, a specialized tissue whose entire job is to burn calories and generate warmth. Research shows that people with hypothyroidism have measurably reduced cold-induced heat production, and that restoring normal thyroid levels brings that heat generation back. Beyond feeling cold, you might notice fatigue, unexplained weight gain, dry skin, or sluggish thinking. A simple blood test measuring TSH (thyroid-stimulating hormone) can flag the problem. The standard normal range is roughly 0.4 to 4.0 mIU/L, though your doctor may interpret results in context of your symptoms and age.
Iron Deficiency Changes Your Core Temperature
Iron-deficiency anemia is another frequent cause, especially in women. When you don’t have enough iron, your body can’t make adequate hemoglobin, the protein in red blood cells that carries oxygen. Less oxygen delivery means less fuel for heat production.
The effect is measurable. In controlled cold-exposure experiments, women with iron-deficiency anemia had lower core body temperatures than women with normal iron levels (36.0°C versus 36.2°C) and consumed less oxygen, meaning their metabolism was running slower. Interestingly, the anemic women also had significantly lower levels of the active thyroid hormones T4 and T3, both at rest and during cold exposure. This suggests iron deficiency doesn’t just limit oxygen delivery; it actually disrupts thyroid function itself, creating a double hit to your body’s heating system.
One important detail: women who were iron-depleted but not yet anemic responded normally to cold. That means your body can tolerate some drop in iron stores before temperature regulation breaks down, but once hemoglobin falls low enough to qualify as anemia, the effect is real and significant.
Circulation Problems and Raynaud’s
If your hands and feet are always freezing while the rest of you feels fine, the issue is likely circulatory rather than metabolic. Blood carries heat from your core to your extremities, and anything that restricts that flow will leave your fingers and toes cold.
Raynaud’s phenomenon is the most recognizable version of this. During an episode, the small blood vessels in your fingers or toes spasm and narrow dramatically in response to cold or stress. Your digits may turn white, then blue, then red as blood flow returns. It affects roughly 3 to 5 percent of the population and is far more common in women. For most people, Raynaud’s is a standalone condition (primary Raynaud’s) that’s uncomfortable but not dangerous. In some cases, it signals an underlying autoimmune condition, which doctors can screen for by examining the tiny blood vessels at the base of your fingernails under magnification.
Certain medications, including stimulants and some migraine drugs, can worsen Raynaud’s or restrict peripheral blood flow on their own. If you’ve noticed your hands and feet getting colder since starting a new medication, that’s worth bringing up.
Body Composition and Heat Retention
Body fat serves as insulation. People with lower body fat percentages lose heat faster because there’s simply less tissue between their warm core and the cold air. Research confirms that insulation capacity correlates positively with body fat percentage, whether you measure it relative to metabolic rate or body surface area. This is why someone who has recently lost a significant amount of weight often notices feeling colder than before, even at temperatures that used to feel comfortable.
Muscle mass matters too. Skeletal muscle generates heat both at rest and during activity. If you’ve lost muscle through inactivity, illness, or aging, your baseline heat production drops. This partly explains why older adults and people who are underweight tend to feel cold more easily.
Vitamin B12 and Nerve-Related Cold Sensations
Vitamin B12 is essential for maintaining the protective coating around your nerves. When levels are low, peripheral neuropathy can develop, causing numbness, tingling, and pain in the hands and feet. Some people with B12 deficiency also experience altered temperature sensation, where their ability to accurately perceive warmth and cold becomes unreliable. While one study found that impaired temperature sensation was a common feature of B12 deficiency due to disrupted sensory nerve function, other research shows the association can be modest depending on the population studied.
B12 deficiency also contributes to a type of anemia (megaloblastic anemia) that reduces oxygen-carrying capacity, similar to iron-deficiency anemia. So low B12 can make you feel cold through two pathways: impaired nerve signaling and reduced heat production from fewer functional red blood cells. Vegetarians, vegans, older adults, and people with digestive conditions that impair absorption are at highest risk.
Chronic Stress Weakens Your Defenses
If your question is less about feeling cold and more about catching colds repeatedly, chronic stress deserves attention. Cortisol, the body’s primary stress hormone, is meant to be anti-inflammatory in short bursts. But when stress is sustained over weeks or months, immune cells actually become resistant to cortisol’s signals. The result is a paradox: your body keeps pumping out stress hormones, but instead of calming the immune system appropriately, it ends up both suppressed and chronically inflamed. Your T-cells and other immune cells change how they respond to these hormones, leaving you more vulnerable to every rhinovirus that comes along.
Why You Keep Catching Colds
Adults typically get two to three upper respiratory infections per year. If you’re consistently above that, several factors could be stacking up against you. Sleep deprivation is one of the strongest predictors of susceptibility. People who regularly sleep fewer than six or seven hours produce fewer antibodies in response to viral exposure and take longer to clear infections.
Indoor air quality plays an underappreciated role. When relative humidity drops below 40 percent, which is common in heated buildings during winter, three things happen simultaneously: the protective mucous layer in your airways dries out and becomes less effective at trapping viruses, airborne virus particles survive longer and travel farther, and exhaled respiratory droplets shrink into smaller particles that float in the air for extended periods. The optimal indoor humidity range for minimizing infection risk is 40 to 60 percent.
Other factors that increase how often you get sick include a weakened immune system from medical conditions or medications, being over 65, and simple exposure patterns. If you commute on public transit, work with children, or share a household with school-age kids, you’re encountering far more viruses than someone who works from home alone. Frequent handwashing remains the single most effective preventive measure, followed by keeping surfaces clean, not sharing utensils, and staying current on vaccinations.
How to Narrow Down Your Cause
Start by noticing the pattern. If your whole body feels cold regardless of the environment, thyroid function and anemia are the first things to check with a blood test. If only your hands and feet are affected, circulation is the more likely issue. If you feel cold and you’ve recently lost weight, changed your diet, or started a new medication, those are strong clues.
A basic panel covering thyroid hormones (TSH and free T4), a complete blood count for anemia, iron levels, and vitamin B12 can rule in or rule out the most common medical causes in a single visit. Many of these conditions overlap and compound each other. Iron deficiency impairs thyroid function, B12 deficiency causes anemia, and chronic stress worsens everything. Identifying even one underlying cause and correcting it often produces a noticeable improvement in how warm you feel day to day.