Feeling cold all the time usually comes down to how your body produces and retains heat. The most common culprits are an underactive thyroid, low iron levels, small body size, poor circulation, or simply not sleeping or eating enough. Sometimes it’s a combination of several factors working together. Normal body temperature ranges from 97°F to 99°F and fluctuates throughout the day, dropping lowest in the early morning, so some variation is expected. But if you’re reaching for a sweater when everyone else is comfortable, something specific is likely going on.
Your Thyroid Sets the Thermostat
The single most common medical cause of chronic cold sensitivity is hypothyroidism, an underactive thyroid gland. Your thyroid produces hormones that affect every cell in your body, controlling the rate at which you burn fats and carbohydrates and directly regulating body temperature. When thyroid hormone levels drop, your metabolism slows and your body generates less heat.
Hypothyroidism develops gradually. Early on, the symptoms (fatigue, weight gain, feeling chilly) are subtle enough that many people chalk them up to aging or stress. Over time, they become harder to ignore. A simple blood test measuring thyroid-stimulating hormone can confirm or rule this out, and it’s one of the first things worth checking if you’re persistently cold without an obvious explanation.
Low Iron and B12 Starve Your Cells of Oxygen
Iron is essential for making hemoglobin, the protein in red blood cells that carries oxygen throughout your body. Without enough iron, your cells don’t get the oxygen they need to produce energy and heat. Cold hands and feet are a hallmark symptom of iron deficiency anemia, often appearing alongside fatigue, pale skin, and shortness of breath.
Vitamin B12 deficiency works through a similar path. Low B12 can cause a type of anemia where your body makes fewer red blood cells, and the ones it does make are abnormally large and less efficient. The result is the same: reduced oxygen delivery, less metabolic heat, and a persistent feeling of being cold. Both deficiencies are detectable through routine blood work and are common in people who menstruate heavily, eat a limited diet, or follow a vegan or vegetarian diet without supplementation.
Body Size and Composition Matter More Than You Think
If you’re lean or small-framed, you’re more likely to feel cold, but the reason isn’t quite what most people assume. Research published in the Journal of Thermal Biology found that fat mass contributes surprisingly little to whole-body insulation. Instead, the key factor is lean mass, meaning muscle. People with more muscle have a higher basal metabolic rate, which means their bodies generate more heat at rest. Larger individuals with more lean mass need to be exposed to colder temperatures before their bodies even activate cold-defense mechanisms like shivering, not because they’re better insulated, but because they’re producing more internal heat to begin with.
This helps explain why two people of similar weight can have very different cold tolerance. Someone with more muscle and less body fat may actually feel warmer than someone with the opposite ratio. It also explains why cold sensitivity often increases after significant weight loss or during periods of undereating, when the body downregulates metabolism to conserve energy.
Circulation Problems and Raynaud’s
If your fingers or toes turn white or blue in cold temperatures or during stress, you may have Raynaud’s phenomenon. In Raynaud’s, the small blood vessels supplying the skin overreact to cold or emotional triggers, clamping down far more than necessary. During an episode, the affected area first turns pale as blood flow drops, then may shift to blue. As circulation returns, the skin reddens and you may feel throbbing, tingling, or swelling.
Primary Raynaud’s (the more common type) isn’t tied to an underlying disease and is more of a nuisance than a danger. It’s most common in women and people living in colder climates. Secondary Raynaud’s is associated with autoimmune conditions and tends to be more severe. Either way, the episodes are unmistakable: your extremities look visibly different from the rest of your skin during a flare.
Medications That Cool You Down
Certain blood pressure medications, particularly beta-blockers, are well known for causing cold hands and feet. These drugs slow the heart rate and can reduce blood flow to the extremities. Research has shown that patients on beta-blockers develop Raynaud’s-like symptoms more frequently than those taking other blood pressure medications. The mechanism involves increased constriction of tiny blood vessels in the hands and a reduced ability of those vessels to open back up when they need to.
If you started feeling persistently cold around the same time you began a new medication, that’s worth mentioning to your prescriber. Other drug classes that can contribute to cold sensitivity include some migraine medications and certain stimulant-based ADHD treatments.
Diabetes and Nerve Damage
Chronically elevated blood sugar damages nerves over time, a condition called diabetic neuropathy. The most common form affects the feet and legs first, then the hands and arms. Damaged nerves lose their ability to accurately sense temperature, which can create a persistent feeling of coldness even when the skin is actually a normal temperature. Symptoms tend to be worse at night and may include numbness, tingling, or burning alongside the cold sensation.
This type of coldness feels different from the others on this list. It’s less about your body failing to produce heat and more about your nerves sending faulty signals. If your feet feel cold to you but warm to the touch, nerve damage is a likely explanation.
Sleep Deprivation Disrupts Your Internal Thermostat
Poor sleep doesn’t just make you tired. It directly interferes with how your body distributes heat. A study in the journal SLEEP found that sleep deprivation causes a striking breakdown in normal temperature regulation. Specifically, it triggers excessive constriction of blood vessels in the hands (making them noticeably cold) while simultaneously allowing too much blood to pool in the lower legs and feet. Normally, these two systems work in sync. After sleep loss, they fall out of coordination.
The researchers linked this to changes in the sympathetic nervous system, the body’s fight-or-flight wiring. Sleep deprivation ramps up the constriction response in some areas while dampening it in others, creating an uneven and inefficient distribution of warmth. If you’ve noticed your hands are ice-cold after a string of bad nights, this is likely why.
Dehydration and Undereating
Your body needs adequate fluid volume to maintain circulation and distribute heat effectively. When you’re dehydrated, blood volume drops, making it harder for your cardiovascular system to simultaneously support your organs and keep your skin warm. The body prioritizes core organs, pulling blood away from the surface and extremities.
Chronic undereating has a similar effect. When calorie intake drops below what your body needs, it reduces metabolic rate to conserve energy. This is an adaptive survival response, but the practical result is that you produce less heat and feel cold more easily. People in prolonged calorie deficits, whether intentional or due to disordered eating, commonly report feeling cold as one of their earliest and most persistent symptoms.
When Multiple Factors Stack Up
For many people, chronic coldness isn’t caused by one dramatic problem but by several mild ones layered together. You might be slightly low on iron, sleep-deprived, undereating by a few hundred calories a day, and spending most of your time sedentary. None of those individually would be enough to explain constant shivering, but together they add up. This is especially common in women, who tend to have lower muscle mass, lose iron through menstruation, and are more prone to thyroid disorders.
A practical first step is basic blood work covering thyroid function, iron levels, B12, and blood sugar. If those come back normal, look at the lifestyle factors: sleep quality, calorie intake, hydration, physical activity, and any medications you’re taking. Cold intolerance is your body’s way of telling you that something in the heat-production or heat-distribution chain isn’t working at full capacity.