Feeling cold all the time usually signals that your body is either not producing enough heat, not delivering it efficiently, or losing it too quickly. The most common culprits are an underactive thyroid, iron deficiency, low body fat, hormonal shifts, and poor circulation. In most cases, a simple blood test can identify or rule out the metabolic causes.
An Underactive Thyroid Slows Your Internal Furnace
Your thyroid gland acts as the thermostat for your metabolism. When it’s underactive, a condition called hypothyroidism, it doesn’t produce enough hormone to maintain your normal basal metabolic rate. Since your metabolic rate is what generates body heat, a sluggish thyroid means less heat production. Cold intolerance is one of the hallmark symptoms, and many people notice it before anything else.
Other signs of hypothyroidism include fatigue, weight gain, dry skin, thinning hair, and brain fog. A blood test measuring your TSH level is the standard screening tool. Normal TSH falls roughly between 0.5 and 4.5 mIU/L. Levels between 4.5 and 10 with normal thyroid hormone levels indicate subclinical hypothyroidism, a milder form that can still cause cold sensitivity. If your TSH is above 10, the diagnosis is more clear-cut. Hypothyroidism is especially common in women over 40, but it can affect anyone at any age.
Iron Deficiency Starves Your Tissues of Oxygen
Iron deficiency is one of the most overlooked reasons people feel perpetually cold. Your body needs iron to make hemoglobin, the protein in red blood cells that carries oxygen from your lungs to every tissue. When iron is low, oxygen delivery drops. That matters for temperature because your cells need oxygen to burn fuel and produce heat through aerobic metabolism. Less oxygen means a lower metabolic rate and less warmth.
The effects go even deeper than that. Iron deficiency also impairs two of your body’s key cold-defense mechanisms: the constriction of blood vessels near the skin’s surface (which normally keeps warm blood near your core) and the ability of your muscles to shiver effectively. Shivering is your body’s emergency heating system, and it depends on iron-containing enzymes inside your muscle cells to generate energy. Without enough iron, even that backup system underperforms.
You don’t need to be severely anemic to feel these effects. Many people with borderline iron stores notice cold hands, fatigue, and pallor. A ferritin level below 45 ng/mL is the recommended threshold for diagnosing iron deficiency in someone with anemia. If your levels are low-normal, say in the 15 to 30 range, you may still feel the impact. Women with heavy periods, vegetarians, and frequent blood donors are at the highest risk.
Low Body Fat Removes Your Insulation
Subcutaneous fat, the layer just beneath your skin, works as a blanket. It reduces conductive heat loss through your skin’s surface and acts as a buffer between your warm core and the cold air around you. People with more body fat lose less heat per unit of skin surface area and shiver less in cold environments than leaner individuals. If you’ve recently lost a significant amount of weight, dropped your body fat percentage through intense training, or are naturally very lean, this insulation loss can make you feel cold in situations that don’t bother others. It’s not a sign of illness, but it explains why someone at a low body weight may reach for a sweater in a room that feels fine to everyone else.
Hormonal Shifts Change Your Thermostat
If you menstruate, your internal temperature shifts throughout your cycle. Estrogen promotes lower body temperatures by increasing heat dissipation, while progesterone pushes temperatures higher. In the days just before ovulation, when estrogen is high and progesterone is still low, basal body temperature dips. After ovulation, during the luteal phase, progesterone rises and body temperature climbs by about 0.5 to 0.8°C. These aren’t random fluctuations. Your brain’s temperature control center actually resets its target in each phase of the cycle.
This means you may genuinely feel colder during the first half of your cycle. Perimenopause and menopause create more dramatic hormonal swings that can make temperature regulation feel unpredictable. Hormonal birth control can also shift the balance, though the direction depends on the formulation.
Raynaud’s Phenomenon and Circulation Problems
If the cold feeling is concentrated in your fingers and toes, and they turn white or blue in response to cold or stress, you may have Raynaud’s phenomenon. During a Raynaud’s episode, the small blood vessels in your extremities spasm and temporarily shut down blood flow. Grabbing a cold glass, reaching into the freezer, or even walking into an air-conditioned building on a warm day can trigger an attack. Emotional stress is another common trigger, because anxiety causes your body to release signaling molecules that narrow blood vessels.
Most people with Raynaud’s have the primary form, which is uncomfortable but harmless. A smaller number have secondary Raynaud’s, which is linked to autoimmune conditions. A doctor can distinguish between the two by examining the tiny blood vessels at the base of your fingernails under magnification. If your cold extremities come with color changes (white, then blue, then red as blood returns), Raynaud’s is worth investigating.
Diabetes and Nerve Damage
Chronically elevated blood sugar damages nerves and the small capillaries that supply them with oxygen and nutrients. This process, called diabetic neuropathy, typically starts in the feet and works its way up to the legs, then the hands and arms. One of the early symptoms is a reduced ability to sense temperature changes. Some people with neuropathy perceive their extremities as feeling persistently cold, even when the skin temperature is normal. This is less about actual heat loss and more about faulty signals from damaged nerves. If you have diabetes or prediabetes and notice cold or numb-feeling feet, it’s worth checking in on your nerve health.
Sleep Deprivation and Chronic Stress
Your brain’s temperature control center sits in the hypothalamus, the same region that regulates sleep. These two systems are deeply intertwined. The hypothalamus receives temperature information from your skin, coordinates heat production through mechanisms like activating brown fat, and simultaneously manages your sleep-wake cycle. When sleep is disrupted, this system starts to malfunction.
Animal research shows that chronic sleep deprivation initially causes a bump in metabolic rate and core temperature, but the body can’t sustain it. Over time, core temperature drops progressively, eventually leading to a state of mild hypothermia. While human studies are less extreme, the pattern holds: poor sleep makes it harder for your body to regulate its temperature. If you’re chronically underslept and always cold, the two problems may be connected.
What to Check First
A basic blood panel can rule in or rule out the most common metabolic causes. The tests worth requesting are TSH (for thyroid function), ferritin and a complete blood count (for iron deficiency and anemia), fasting blood glucose or HbA1c (for diabetes), and vitamin B12 if you’re vegetarian, over 50, or have tingling in your hands and feet. B12 deficiency causes anemia similar to iron deficiency and can also damage the nerves responsible for sensation in your extremities.
If your labs come back normal, consider the non-medical explanations: low body fat, hormonal cycling, poor sleep, or simply spending too much time in air-conditioned environments without adapting. Some people also run naturally cooler than others, and a core temperature slightly below the old 98.6°F benchmark is increasingly recognized as common and normal. But persistent, unexplained cold intolerance that’s new or worsening deserves a closer look, because the treatable causes are straightforward to identify and manage.