Some people feel colder than others because of real, measurable differences in how their bodies produce and distribute heat. Your metabolic rate, body composition, hormone levels, blood circulation, and even your iron stores all play a role in whether you’re the person reaching for a sweater when everyone else is comfortable. These aren’t just quirks of personality. They reflect genuine variation in your body’s internal heating system.
Your Metabolism Sets the Baseline
Your body is essentially a furnace. About 60% of the energy you burn each day goes toward basic functions like breathing, pumping blood, and maintaining organs, even when you’re doing nothing. Roughly 60% of the heat generated during these metabolic processes is specifically used to maintain body temperature. The remaining heat comes from physical activity (about 30% of daily energy use) and digesting food (about 10%).
This means people with a higher basal metabolic rate produce more internal heat as a byproduct of simply being alive. Two people sitting in the same room can have meaningfully different metabolic rates based on their age, size, muscle mass, and genetics. The person with the slower metabolism is generating less heat at baseline and will feel the chill sooner.
Muscle Matters More Than You’d Think
Skeletal muscle is one of the body’s most important heat-generating tissues. When you’re cold, your muscles contract involuntarily (shivering) to produce warmth. But muscle also generates heat without shivering, through internal calcium cycling processes that burn energy and release heat as a byproduct. This “non-shivering” heat production works alongside brown fat to keep you warm in cool environments.
People with more muscle mass have a larger built-in heating system. This is one reason why someone who is very lean but muscular may tolerate cold better than someone with less muscle, even if both weigh the same. Body fat does provide insulation, slowing heat loss through the skin, but it doesn’t actively generate heat the way muscle and brown fat do. So the balance between your muscle mass and your fat stores shapes both how much heat you make and how quickly you lose it.
Brown Fat: A Hidden Heat Source
Most adults have deposits of brown fat, primarily in the neck region, that can be activated by cold exposure. Unlike regular white fat, which stores energy, brown fat contains a specialized protein that lets it burn fuel at a high rate specifically to produce heat. Think of it as a space heater tucked under your skin. Some people have more active brown fat than others, and this variation contributes to differences in cold tolerance. People who are regularly exposed to cool temperatures tend to have more active brown fat, while those who spend most of their time in heated environments may have less.
Thyroid Hormones Control the Thermostat
Your thyroid gland acts as the body’s thermostat controller. Thyroid hormones ramp up energy use across nearly every tissue, increasing the rate at which your cells burn fuel and produce heat. They also amplify the effects of your sympathetic nervous system (the “fight or flight” system), which controls how blood vessels constrict and how actively brown fat burns.
When thyroid function is low, a condition called hypothyroidism, the whole system slows down. Heat production drops, and cold intolerance is one of the hallmark symptoms. Even mildly low thyroid function can leave you reaching for extra layers. Hypothyroidism is common, affecting an estimated 5% of the population, and many cases go undiagnosed for years because the symptoms creep in gradually.
Why Women Often Feel Colder
The stereotype that women feel colder than men has a physiological basis. Women tend to have lower muscle mass relative to body size, which means less active heat generation. They also tend to have a stronger blood vessel constriction response in their extremities, pulling warm blood away from the skin and toward the core. This keeps internal organs warm but leaves fingers and toes noticeably cold.
Estrogen plays a direct role in this equation. It influences peripheral blood flow: in one study, estrogen increased forearm blood flow from 2.4 to 3.9 milliliters per 100 milliliters of tissue per minute and cut vascular resistance nearly in half. This means fluctuating estrogen levels across the menstrual cycle, during menopause, or with hormonal birth control can shift how warm or cold your hands and feet feel from week to week. When estrogen drops, blood vessels constrict more, and extremities get colder.
Iron Deficiency and Feeling Cold
If you’re consistently colder than everyone around you, low iron is worth considering. Iron deficiency impairs your body’s ability to regulate temperature through two separate pathways. First, it disrupts thyroid function, which reduces overall heat production. Second, anemia (low red blood cell count from iron deficiency) creates a tug-of-war in your circulation: your body needs to deliver oxygen to tissues but also wants to restrict blood flow to the skin to prevent heat loss. It can’t do both well, so thermoregulation suffers.
Research consistently identifies anemia as a central reason why iron-deficient people struggle to stay warm when exposed to cold. Women of reproductive age, vegetarians, and frequent blood donors are at higher risk for low iron, which partly explains why these groups report more cold sensitivity.
Circulation Problems and Raynaud’s
Some people don’t just feel cold. Their fingers and toes turn white or blue, go numb, and sting painfully when they warm up. This is Raynaud’s phenomenon, a condition where small blood vessels in the extremities spasm shut in response to cold or stress, cutting off blood flow far more aggressively than normal. Affected areas typically turn white first, then blue, then red as blood flow returns.
Raynaud’s affects up to 5-10% of the general population and is much more common in women. Over time, the affected blood vessels can thicken slightly, making episodes worse. For most people it’s uncomfortable but not dangerous. In some cases, though, it signals an underlying autoimmune condition, so persistent episodes are worth mentioning to a doctor.
Your Body Can Learn to Handle Cold
Cold tolerance isn’t entirely fixed. Your body adapts to repeated cold exposure through a process called cold habituation. The timeline is surprisingly fast: people typically report reduced cold sensation after just one or two exposures, and cold-related pain starts to decrease by the second to fifth day of repeated exposure.
With habituation, your body dials back its alarm response. Blood vessel constriction becomes less extreme, blood pressure spikes are smaller, and stress hormone release decreases. This doesn’t mean you stop losing heat. Rather, your nervous system stops overreacting to the cold signal. People who work outdoors, swim in cold water, or keep their homes cooler develop this adaptation naturally. People who spend most of their time in well-heated environments never trigger it, which is one reason the same temperature can feel brutal to one person and mild to another.
Age, Hydration, and Daily Rhythms
Older adults feel colder for several compounding reasons. Metabolic rate naturally declines with age, muscle mass decreases, skin thins (reducing insulation), and blood vessel responses become less effective. The body’s ability to constrict blood vessels in the cold weakens, meaning older adults lose heat faster while producing less of it.
Hydration also plays an underappreciated role. When you’re dehydrated, both your blood volume and the water content inside your cells drop. This makes it harder for your cardiovascular system to simultaneously deliver oxygen to working tissues and route warm blood to your skin. The result is impaired temperature regulation. While most research focuses on overheating during dehydration, the underlying principle works in both directions: lower blood volume means less efficient heat distribution throughout the body.
Your body temperature also fluctuates naturally by about 1°C (roughly 1.8°F) over a 24-hour cycle, dropping lowest in the early morning hours and peaking in the late afternoon. This rhythm persists even during complete bed rest, meaning it’s driven by your internal clock rather than physical activity. It’s one reason you might feel perfectly comfortable at 8 PM but chilly at 6 AM in the same room at the same thermostat setting.