You catch a cold by inhaling tiny virus-laden particles from the air or, less commonly, by touching a contaminated surface and then touching your nose or eyes. The virus needs to reach the lining of your nasal passages, where it latches onto cells and begins replicating. Adults average two to three colds per year, while children pick up five to eight, largely because their immune systems haven’t encountered as many viral strains yet.
How the Virus Gets Into Your Body
Rhinoviruses, the cause of most colds, spread primarily through the air. When a sick person coughs, sneezes, talks, or even breathes, they release aerosol particles containing the virus. A 2023 review in the American Journal of Infection Control found moderate evidence that airborne transmission in indoor settings is the dominant route, while transmission through hand contact and contaminated surfaces plays a secondary role.
The virus is remarkably efficient at establishing infection. It needs only a tiny number of viral particles to take hold, especially when delivered directly to the nasal lining via a sneeze or inhaled droplet. Once a rhinovirus particle lands on the surface of your airway cells, it binds to a receptor and gets pulled inside the cell through a process called endocytosis. From there, it releases its genetic material and hijacks the cell’s machinery to make copies of itself. Within hours, newly minted virus particles burst out to infect neighboring cells, and the cycle accelerates.
Why Indoor Air Makes It Easier
Cold and flu season peaks in winter partly because people spend more time indoors in close quarters, but the air itself also matters. Research at Yale University showed that low humidity impairs your respiratory defenses in three distinct ways. First, the tiny hair-like structures lining your airways (cilia) become less effective at sweeping out viral particles and mucus. Second, airway cells lose some of their ability to repair virus-caused damage. Third, the signaling system that warns neighboring cells about an incoming virus fails to activate properly. Dry, heated indoor air during winter creates exactly these conditions.
Temperature plays a role too. Studies on mouse airway cells infected with rhinovirus found that antiviral defenses were significantly stronger at core body temperature (37°C) than at the cooler temperature typical of nasal passages (33°C). When you breathe cold outdoor air, your nasal lining drops in temperature, giving the virus a window where your local immune response is weaker. This is one reason the old advice about bundling up in cold weather has a grain of biological truth: it’s not the cold itself that makes you sick, but the cooler nasal environment reduces your ability to fight off a virus you’ve already been exposed to.
Factors That Raise Your Risk
Sleep is one of the strongest predictors of whether you’ll catch a cold after exposure. A study published in JAMA Internal Medicine deliberately exposed volunteers to rhinovirus and tracked who got sick. People sleeping fewer than seven hours per night were nearly three times more likely to develop a cold than those getting eight hours or more. Even more striking, participants who slept restlessly (spending less than 92% of their time in bed actually asleep) were 5.5 times more likely to get infected than sound sleepers.
Other factors that weaken your defenses and increase your chances of catching a cold include:
- Chronic stress: sustained psychological stress suppresses the immune cells that patrol your airways
- Close contact with children: young kids shed large amounts of virus and frequently touch shared surfaces
- Crowded indoor spaces: offices, classrooms, and public transit concentrate airborne particles
- Smoking: cigarette smoke damages the cilia that clear viruses from your airways
- Touching your face: the average person touches their face 16 to 23 times per hour, providing a direct route from contaminated hands to the nose or eyes
How Quickly Symptoms Appear
Once the virus establishes itself, symptoms typically show up between 12 hours and three days after exposure. The first signs are usually a scratchy throat and a runny nose. Within a day or two, congestion, sneezing, and mild fatigue set in. A cough often develops later as mucus drains from the sinuses.
Viral shedding, the period during which you’re producing and releasing virus, usually begins within 24 to 48 hours of infection, often before you feel any symptoms at all. This pre-symptomatic shedding is one reason colds spread so effectively: you can pass the virus to others before you even know you’re sick. Shedding peaks between days three and six, then tapers off. Most people stop shedding virus after four to five days, though some continue for up to nine days.
Why Some People Catch Colds More Often
There are over 160 known strains of rhinovirus, and immunity to one doesn’t protect you against the others. Each time you encounter a new strain, your immune system essentially starts from scratch. Children get sick more frequently because they’ve built up immunity to fewer strains. Adults who work with young children or in healthcare settings also tend to catch more colds simply due to higher exposure.
Your baseline immune function matters too. People who exercise moderately, sleep well, and manage stress tend to mount faster antiviral responses when exposed. On the other hand, those who are sleep-deprived, sedentary, or under chronic stress have slower immune reactions, giving the virus more time to replicate before the body’s defenses kick in. The difference between “exposed but fine” and “exposed and sick for a week” often comes down to what your immune system was doing in the hours before the virus arrived.