A cold house doesn’t directly cause infections, but it creates conditions that make you more vulnerable to getting sick. Cooler air weakens your body’s frontline immune defenses, raises blood pressure, and can foster mold growth that triggers respiratory problems. The World Health Organization recommends keeping indoor temperatures at or above 18°C (about 64°F) to protect health during cold seasons.
How Cold Air Weakens Your Immune Defenses
The connection between cold environments and illness isn’t just folk wisdom. Research from Yale University published in the Proceedings of the National Academy of Sciences showed that the common cold virus replicates more efficiently at cooler temperatures (33 to 35°C) than at core body temperature (37°C). The reason isn’t that cold makes the virus stronger. It’s that cold makes your immune response weaker.
When the temperature in your airway cells drops even a few degrees, the virus-sensing machinery inside those cells becomes less active. At body temperature, immune sensors ramp up about 65% more activity compared to the cooler temperatures found in your nasal passages. This translates into stronger antiviral signaling, more production of protective proteins called interferons, and ultimately better containment of the virus. In a cold house, you’re breathing cooler air for hours at a time, which means the tissues in your nose and upper airway stay at temperatures where your defenses are sluggish.
Cold exposure also slows down the physical cleaning system in your airways. The lining of your nose and throat is coated in mucus that traps pathogens and sweeps them out. Research on cold exposure found that this mucus transport slows by about 24% in cold conditions compared to comfortable temperatures. That means inhaled bacteria and viruses linger longer in your airways, giving them a better chance to take hold.
Blood Pressure and Heart Strain
Cold indoor temperatures don’t just affect your respiratory system. They put measurable stress on your cardiovascular system. When your body senses cold, blood vessels near the skin constrict to conserve heat. This raises blood pressure. Randomized controlled trials have shown that improving indoor temperatures can reduce systolic blood pressure by roughly 5.8 mmHg, a meaningful change for anyone already at risk for heart disease or stroke.
This isn’t a one-time spike. If you spend every winter in a poorly heated home, you’re experiencing repeated blood pressure increases during your waking hours for months at a stretch. Observational studies across 16 countries have confirmed a consistent link between low indoor temperatures and elevated blood pressure. For people with existing hypertension or heart conditions, a chronically cold home compounds their risk.
Mold Thrives in Cold, Damp Homes
One of the less obvious ways a cold house makes you sick is through mold. Many people assume mold needs warmth to grow, but that’s a misconception. Mold primarily needs moisture and a surface to grow on. Cold homes are prone to condensation: warm air from cooking, showering, or even breathing hits cold walls and windows, creating the persistent dampness mold needs to flourish.
Mold exposure triggers allergic reactions in many people, with symptoms including itchy or watery eyes, runny nose, coughing, wheezing, and a scratchy throat. People with asthma, compromised immune systems, or existing allergies are at higher risk for serious reactions. In rare cases, toxins produced by certain mold species can cause severe illness. The problem compounds over time: a cold home that stays damp through the winter can develop significant mold growth in walls, window frames, and poorly ventilated corners that continues to release spores long after you notice it.
Mental Health Effects
Living in a cold home takes a psychological toll as well. The WHO’s systematic review of housing and health identified depression as a priority health outcome linked to cold indoor environments. A randomized trial in New Zealand found that insulating homes, which raised indoor temperatures, reduced the odds of poor mental health among residents. The effect makes intuitive sense: chronic physical discomfort, poor sleep from being cold at night, and the stress of high heating bills all feed into anxiety and low mood.
The evidence is mixed on how large this effect is. Some trials found clear mental health improvements after homes were insulated, while others did not detect significant changes. But the pattern across multiple studies suggests that thermal discomfort is at minimum a contributing factor to poor mental wellbeing, particularly during long winters.
Older Adults Face the Greatest Risk
Cold homes are dangerous for everyone, but older adults are especially vulnerable. The National Institute on Aging warns that even mildly cool homes with temperatures between 60 and 65°F (15.5 to 18°C) can lead to hypothermia in older people. Aging reduces the body’s ability to regulate temperature, and many older adults don’t feel cold as intensely, meaning they may not realize their home has dropped to unsafe levels.
The stakes are high. Research in the United Kingdom linked cold housing to an estimated 50,000 excess winter deaths annually. People living in the coldest homes had roughly a 50% higher risk of dying in winter compared to summer, while those in the warmest homes saw only a 30% increase. That gap represents thousands of preventable deaths driven largely by cardiovascular and respiratory complications from cold exposure.
What Temperature to Aim For
The WHO’s recommendation of 18°C (64°F) is the baseline for healthy adults. For households with infants, elderly residents, or anyone with chronic illness, warmer temperatures are safer. Bedrooms should stay warm enough that you’re not shivering under blankets, since prolonged cold exposure during sleep affects blood pressure and immune function just as it does during waking hours.
If heating costs make it difficult to warm your entire home, focus on the rooms where you spend the most time. Keep bedroom and living room doors closed to retain heat. Insulation is the single most effective long-term investment: proper loft and wall insulation reduces heat loss dramatically, and trials have shown it improves respiratory symptoms, mental health, and general wellbeing. Heavy curtains over windows, draft excluders at doors, and rugs on bare floors all help retain warmth in the short term.
Ventilation still matters even in cold weather. Briefly opening windows or using extractor fans in kitchens and bathrooms helps remove excess moisture without cooling the house significantly, reducing the condensation that feeds mold growth. The goal is a home that stays warm and dry, not one that’s sealed tight and damp.