You get a cold when a respiratory virus, most often a rhinovirus, enters your nose or eyes and latches onto cells lining your airways. This happens through three main routes: inhaling droplets someone else coughs or sneezes into the air, touching a contaminated surface and then touching your face, or being close enough to a sick person that their exhaled particles reach your nose or mouth. Adults average two to three colds per year, while children typically catch even more.
How the Virus Gets Inside Your Cells
Rhinoviruses cause the majority of colds, and over 100 different strains exist. About 90% of those strains use a single molecule on the surface of your airway cells as their entry point. The virus essentially hijacks a protein your immune cells normally use to communicate with each other, docking onto it like a key fitting a lock. Once attached, the virus slips inside the cell, takes over its machinery, and starts producing copies of itself.
One reason colds spread so easily is that your own immune response can work against you during an infection. When your body detects the virus and triggers inflammation, the inflamed cells actually produce more of that surface protein the virus needs to enter. So as your immune system ramps up its defense in one area, neighboring cells become easier targets.
The Three Ways Colds Spread
The most common transmission route is respiratory droplets. When a person with a cold coughs, sneezes, or even talks, they release virus-laden droplets that can land on your mouth, nose, or eyes if you’re within a few feet. Larger droplets settle quickly, which is why close contact matters most.
Surface contact is the second major route. Rhinoviruses can survive on doorknobs, phones, keyboards, and countertops for hours. You pick up the virus on your fingers and deliver it yourself when you rub your eyes or touch your nose. Studies suggest people touch their faces dozens of times per hour without realizing it, making this route surprisingly efficient.
The third route involves smaller airborne particles that can linger in the air longer, especially in poorly ventilated rooms. This is less dominant for rhinovirus than for viruses like measles or tuberculosis, but enclosed spaces with recirculated air (offices, classrooms, airplane cabins) still raise your exposure risk.
Why Colds Peak in Winter
Cold weather itself doesn’t cause a cold, but the conditions that come with it do. Research published in the Proceedings of the National Academy of Sciences found that dry air impairs three of your body’s frontline defenses simultaneously. First, it slows mucociliary clearance, the process where tiny hairs in your airways sweep mucus (and trapped viruses) out of your respiratory tract. Second, it suppresses the genes your cells activate to fight viral invaders. Third, it reduces your tissue’s ability to repair damage from infection.
The result is that breathing dry, heated indoor air during winter months lets viruses gain a stronger foothold before your body mounts an effective response. Cold temperatures also drive people indoors, where close contact and shared surfaces create ideal conditions for the virus to jump between hosts.
People Who Seem Healthy Can Still Spread It
One of the trickiest aspects of cold transmission is that many infected people never feel sick. Studies of community virus testing have found that anywhere from half to the vast majority of people who test positive for a respiratory virus report no symptoms at all. These individuals still shed virus particles, meaning they can pass the infection to others through normal activities like talking, sharing utensils, or touching communal surfaces. You can catch a cold from someone who has no idea they’re carrying the virus.
What Makes You More Likely to Catch One
Sleep is one of the strongest predictors of cold susceptibility. A study from Carnegie Mellon University deliberately exposed volunteers to rhinovirus and tracked who got sick. People who slept six hours or less per night were 4.2 times more likely to develop a cold than those sleeping more than seven hours. For those getting fewer than five hours, the risk jumped to 4.5 times higher. This held true even after accounting for other factors like stress, age, and smoking.
Chronic stress also suppresses immune function in ways that make infection more likely. When your body stays in a heightened stress state for weeks or months, it produces sustained levels of stress hormones that dampen your immune cells’ ability to respond to new threats. Smokers face higher risk too, because cigarette smoke damages the protective lining of the airways, essentially removing one of the barriers the virus needs to get past.
Children get more colds partly because their immune systems haven’t encountered as many viral strains yet. Each infection teaches the immune system to recognize a specific strain, but with over 100 rhinovirus types circulating, it takes years to build a broad defense. Daycare and school environments, where kids share toys and sit in close quarters, accelerate exposure.
Handwashing Beats Hand Sanitizer for Colds
Rhinoviruses are nonenveloped viruses, meaning they lack the fatty outer coating that makes some other viruses vulnerable to alcohol. Research comparing the two hygiene methods found that alcohol-based hand sanitizers are significantly less effective against nonenveloped viruses. Washing with soap and water removed more than 99.999% of nonenveloped virus particles from hands, while alcohol-based sanitizers failed to inactivate the same viruses effectively even after three minutes of contact.
This doesn’t mean sanitizer is useless. It works well against enveloped viruses like influenza. But if your primary concern is avoiding colds, soap and water is the better choice. Wash for at least 20 seconds, and pay attention to fingertips and the spaces between fingers, where virus particles tend to linger.
Beyond hand hygiene, keeping indoor humidity between 40% and 60% helps maintain your airway defenses. A simple room humidifier during winter months counteracts the dry air that weakens your mucociliary clearance. Prioritizing seven or more hours of sleep per night is one of the most impactful things you can do, given how dramatically sleep deprivation increases susceptibility. And while it sounds obvious, keeping your hands away from your face breaks the surface-to-mucous-membrane chain that accounts for a large share of infections.