Cold weather doesn’t directly cause infections, but it creates the perfect conditions for viruses to spread and puts real stress on your body. The illnesses linked to cold exposure fall into two categories: infections that spike in winter because of how cold air helps viruses thrive, and direct injuries to your body from the cold itself.
Why Colds and Flu Spike in Winter
The common cold virus, rhinovirus, replicates most efficiently at temperatures between 33 and 35°C, which is the temperature inside your nasal passages. That’s a few degrees cooler than your core body temperature of 37°C. When you breathe cold air, your nose drops even further into that sweet spot, and your immune defenses in the nasal lining weaken at the same time. So while “catching a cold” from cold weather is technically a myth, the cold genuinely helps the virus do its job once it’s in your nose.
Influenza follows a similar pattern but for different reasons. The flu virus is more stable and survives longer in cold, dry air. In lab studies, flu transmission was highly efficient at 5°C but blocked or nearly absent at 30°C. Low humidity, common in winter, also plays a major role. Dry air at 20 to 35% relative humidity favors flu spread far more than humid conditions at 50% or above. Dry air also causes respiratory droplets to evaporate faster, shrinking them so they float longer and travel farther before someone else inhales them. This is a big reason flu season lines up so reliably with winter months.
Cold Air and Breathing Problems
If you have asthma, breathing cold air can trigger your airways to narrow. This happens because inhaling cold, dry air pulls heat and moisture from the lining of your airways, creating a temporary change in the salt concentration of the tissue. That shift causes the muscles around your airways to tighten. The result is coughing, wheezing, and shortness of breath that can hit within minutes of stepping outside. Even people without asthma sometimes notice chest tightness or a burning sensation in their lungs during intense cold, though the effect is much milder.
Heart Attack and Stroke Risk
Cold weather forces your heart to work harder. When your body temperature drops, blood vessels near the skin constrict to conserve heat, which raises blood pressure. For people with existing heart disease or risk factors, this added strain matters. A large multi-country study found that a 5°C drop in air temperature was associated with a 12% increase in hospital admissions for heart attacks and a 7% increase for strokes. The risk is highest during sudden cold snaps and in people who are exerting themselves outdoors, like shoveling snow.
Hypothermia
Hypothermia sets in when your core body temperature drops below 35°C (95°F). It doesn’t require extreme arctic conditions. Prolonged exposure to cool, wet weather, falling into cold water, or simply being underdressed on a windy day can all do it. There are three stages:
- Mild (32 to 35°C / 90 to 95°F): Shivering, difficulty with coordination, and confusion. Your body is still actively trying to warm itself.
- Moderate (28 to 32°C / 82 to 90°F): Shivering may actually stop, which is a dangerous sign. Confusion worsens, speech slurs, and drowsiness sets in.
- Severe (below 28°C / 82°F): Loss of consciousness, very slow breathing and heart rate, and risk of cardiac arrest.
The key danger with hypothermia is that confused people often don’t realize how cold they are. Older adults, young children, and anyone who is wet or intoxicated are especially vulnerable.
Frostbite
Frostbite is actual freezing of skin and underlying tissue. It progresses through three stages. Frostnip, the mildest form, turns the skin red or pale and causes stinging or soreness. Surface frostbite brings a pins-and-needles sensation, and the skin may look waxy. Deep frostbite causes complete numbness as tissue freezes solid. A day or two after exposure, large blisters form. In the worst cases, frozen skin turns black as the cells die.
Fingers, toes, ears, and the nose are most vulnerable because they’re farthest from your core and have the least insulation. Wind dramatically accelerates the process. If you suspect frostbite, get out of the cold immediately. Permanent tissue damage is possible once freezing reaches deeper layers.
Trench Foot
Trench foot is a non-freezing injury that develops when feet stay cold and wet for extended periods. Unlike frostbite, it can happen in temperatures as warm as 16°C (60°F), and damage can begin in as little as 10 to 14 hours. The combination of cold and moisture destroys tiny blood vessels in the feet, leading to swelling, pain, numbness, and eventually tissue breakdown. It’s a particular risk for hikers, outdoor workers, and anyone whose shoes stay wet for long stretches.
Chilblains
Chilblains are small, itchy, swollen patches that appear on fingers, toes, heels, or ears after repeated exposure to cold, damp air. They form when blood vessels near the skin’s surface constrict in the cold and then struggle to reopen properly, causing inflammation. The affected skin turns red or purple, burns or itches, and may develop small blisters. Chilblains typically clear up on their own within one to three weeks once you avoid the cold, but they tend to come back each winter in people who are prone to them.
Raynaud’s Attacks
Raynaud’s phenomenon causes the small arteries in your fingers and toes to spasm when exposed to cold, cutting off blood flow far more aggressively than normal. During an attack, the affected fingers turn white as blood flow stops, then blue as oxygen depletes, and finally red as circulation returns. The whole episode can last minutes to hours and comes with numbness, tingling, and sometimes pain. About 5 to 10% of the general population has some degree of Raynaud’s. For most people it’s uncomfortable but harmless. In people with autoimmune conditions, however, severe attacks can damage tissue over time.
Keeping your hands and feet warm, wearing layers, and avoiding sudden temperature changes are the simplest ways to reduce the frequency of attacks.