Feeling cold all the time usually signals that your body is struggling with one of three things: producing enough heat, delivering warm blood to your tissues, or regulating temperature through your brain and hormones. The most common medical causes are an underactive thyroid, iron deficiency anemia, and poor circulation, but body composition, hydration, and even sleep habits play a role too.
Your Thyroid Sets the Thermostat
The single most common medical explanation for chronic coldness is hypothyroidism, a condition where your thyroid gland doesn’t produce enough hormones. Thyroid hormones control your basal metabolic rate, which is essentially how much energy your body burns at rest. When levels drop, your internal furnace turns down.
The mechanism is surprisingly direct. Thyroid hormones stimulate your cells to produce energy and, as a byproduct, heat. They also activate a special type of fat called brown adipose tissue, which exists specifically to convert calories into warmth rather than storing them. In people with low thyroid function, brown fat cells can’t do their job properly because they depend on thyroid hormone to power the protein that short-circuits normal energy production and releases heat instead. Cold intolerance is one of the hallmark symptoms of hypothyroidism, alongside fatigue, weight gain, dry skin, and sluggish thinking. A simple blood test measuring thyroid-stimulating hormone (TSH) can confirm or rule it out.
Iron Deficiency Starves Your Tissues of Oxygen
Iron deficiency anemia is another frequent culprit, especially in women with heavy periods, vegetarians, and people with digestive conditions that impair nutrient absorption. When you don’t have enough iron, your body can’t make adequate hemoglobin, the molecule in red blood cells that carries oxygen. Less oxygen reaching your tissues means less fuel for heat production.
But iron deficiency hits thermoregulation from two directions. It impairs thyroid function directly, reducing your heat output. At the same time, your body faces a cruel tradeoff: it needs to keep blood flowing to vital organs that are oxygen-starved, but it also needs to restrict blood flow to the skin and extremities to prevent heat from escaping. The result is cold hands, cold feet, and a general inability to warm up. One published review concluded that anemia is a central component of the temperature regulation failure seen in iron-deficient individuals. Your doctor can check iron levels with a complete blood count and a ferritin test.
B12 Deficiency and Nerve Damage
Vitamin B12 deficiency causes a type of anemia similar to iron deficiency, but it also damages nerves over time. That nerve damage can distort how your body senses and responds to temperature. In one documented case, a patient rated their chronic feeling of coldness at 8 out of 10 before starting B12 treatment. After six months of supplementation, that score dropped to zero. B12 deficiency is common in older adults, people on certain acid-reducing medications, and those who eat little or no animal products.
Poor Circulation to the Extremities
If your coldness is concentrated in your hands and feet rather than your whole body, circulation problems are worth investigating. Two conditions stand out.
Raynaud’s Phenomenon
Raynaud’s causes the small blood vessels in your fingers and toes to overreact to cold or stress, clamping down and dramatically reducing blood flow. During an episode, affected fingers typically turn white or blue and feel numb before flushing red and tingling as blood returns. The primary form, which affects roughly 3 to 5 percent of the population, isn’t linked to any other disease and tends to appear in younger adults. Secondary Raynaud’s develops later, usually around age 40, as a complication of autoimmune conditions or other illnesses.
Peripheral Artery Disease
Peripheral artery disease (PAD) is a buildup of fatty plaque inside the arteries that supply your legs and arms. As the arteries narrow, less warm blood reaches your lower legs and feet. One telltale sign is coldness in one foot compared to the other. PAD is more common in people over 50, smokers, and those with diabetes or high blood pressure. Unlike Raynaud’s, which comes and goes in episodes, PAD tends to cause persistent symptoms that worsen over time, including leg pain during walking and slow-healing wounds.
Low Body Fat Removes Your Insulation
Subcutaneous fat, the layer just beneath your skin, acts as a built-in blanket. When body fat drops below healthy ranges, you lose that insulation and become noticeably more sensitive to cool temperatures. Healthy body fat sits between 18 and 24 percent for men and 25 to 31 percent for women, though age and activity level shift those numbers. People who lose significant weight often report feeling cold in situations that never bothered them before. Very lean athletes experience the same thing. This type of cold sensitivity is a straightforward physics problem: less insulation means faster heat loss through the skin.
Dehydration Quietly Lowers Your Core Temperature
Most people don’t connect hydration with body temperature, but even mild dehydration shrinks your blood volume. With less blood circulating, your body struggles to move warmth from your core to your skin and extremities. The fluid loss makes blood more concentrated while reducing overall volume, a combination that impairs your cardiovascular system’s ability to support both normal metabolism and temperature regulation at the same time. If you consistently drink less water than you need, chronic mild dehydration could be making you feel colder than you should.
Sleep Deprivation Disrupts Temperature Control
The part of your brain that controls sleep and the part that controls body temperature are, in large part, the same structure: a region in the front of the hypothalamus called the preoptic area. Sleep and body temperature are tightly interconnected. Your core temperature naturally drops as you fall asleep, and this cooling process is part of what triggers and maintains deep sleep.
When sleep is fragmented or cut short, this coordinated cycle breaks down. Animal studies show that disrupted sleep prevents the normal temperature fluctuations the brain relies on, and that the neurons controlling sleep directly overlap with those managing heat production. While research in humans is still catching up, the implication is clear: chronic poor sleep can impair your brain’s ability to keep your body temperature stable, potentially leaving you feeling cold during the day.
Other Factors That Contribute
Several less obvious factors can tip the scales toward chronic coldness:
- Diabetes: Long-term high blood sugar damages peripheral nerves and small blood vessels, reducing blood flow to the hands and feet and distorting temperature sensation.
- Age: Older adults lose muscle mass, produce less metabolic heat, and often have thinner skin with less insulating fat.
- Low calorie intake: Your body generates heat as a byproduct of digesting and metabolizing food. Eating too few calories, whether intentionally or not, reduces this heat production.
- Smaller body size: People with a higher surface-area-to-volume ratio lose heat faster. This is one reason women tend to report feeling cold more often than men.
What Testing Looks Like
If feeling cold is persistent and bothering you, a doctor will typically start with blood work. The most useful initial tests check thyroid function (TSH), red blood cell counts and hemoglobin (a complete blood count), iron stores (ferritin), and B12 levels. These four tests together can identify or rule out the most common treatable causes. If results are normal and your coldness is concentrated in your hands or feet, your doctor may evaluate you for Raynaud’s or check the pulses and blood pressure in your legs to screen for peripheral artery disease.
It’s also worth noting that “normal” body temperature is not a fixed 98.6°F. A systematic review of published data found the average oral temperature is closer to 97.9°F (36.6°C), with a normal range spanning roughly 97.1°F to 98.6°F. Some people simply run cooler than others without anything being wrong. The distinction that matters is whether your cold sensitivity has changed, whether it’s new or worsening, or whether it’s accompanied by other symptoms like fatigue, hair loss, or unexplained weight changes.