What causes a cold?

Colds are one of the most common illnesses, affecting people of all ages. They are caused by viruses and easily spread from person to person. But what exactly leads to catching a cold? Here we will explore the causes of the common cold, from how the cold viruses spread to risk factors that make some people more susceptible.

Table of Contents

How do cold viruses spread?

Colds are caused by viruses. There are over 200 types of viruses that can cause the common cold, with rhinoviruses being the most common. These cold viruses are found in the mucus of the nose and throat of someone who is infected. When that person talks, coughs, or sneezes, virus particles get into tiny droplets that are launched into the air. If these droplets come into contact with the eyes, mouth or nose of another person, the virus can be transmitted. The viruses can also spread by touching contaminated surfaces like doorknobs, phones, or keyboards and then touching your face before washing your hands.

Because cold viruses are so contagious, it’s no surprise they are widespread. Adults get around 2-3 colds per year on average and children can get up to 6-8 colds annually. Colds occur more frequently in the fall and winter when people spend more time indoors in close contact. But it is possible to get a cold any time of the year.

Who is most at risk for catching a cold?

While anyone can get a cold, some factors make certain individuals more prone to catching and spreading colds:

Age – Children get more colds than adults because their immune systems are still developing. Being around other children in daycares and schools also increases exposure.

Weakened immunity – Those with weakened immune systems due to conditions like HIV/AIDS or cancer treatments can be more susceptible to prolonged and severe colds.
Smoking – The chemicals from cigarette smoke damage the hairs in the nose that normally trap viruses and keep them from infecting the body. Smokers are therefore more vulnerable to cold viruses.
Asthma – The airway inflammation associated with asthma can make sufferers more likely to develop infections like colds that further irritate the airways.

Stress – High stress is associated with greater susceptibility to colds and can even lengthen the duration of symptoms.
Lack of sleep – Not getting enough sleep lowers the body’s ability to fend off viruses and infection.

How do cold symptoms develop?

Once cold viruses manage to enter the body, they start replicating rapidly. It takes around 1-3 days from initial exposure for the first symptoms to arise. Here’s a look at what’s happening inside the body:

Days 1-2: The viruses multiply in the nasal passages and upper throat. This irritates the mucus membranes, causing a runny nose, congestion, sneezing, and a sore throat.
Days 3-4: Viruses penetrate deeper into the upper airways and inflame the nasal tissues. Mucus production increases.
Days 5-7: The immune system’s inflammatory response is in full effect. Symptoms like malaise, fever, headaches, and body aches emerge.

Days 8-10: Symptoms typically peak around days 8-10. Secondary bacterial infections can sometimes occur at this point, prolonging the illness.
Days 11-14: Finally, the immune system gains the upper hand. Symptoms gradually improve and the viruses are cleared from the body.

The severity and duration of symptoms can vary. Most colds run their course within 7-10 days. However, some last for up to two weeks. The cough that lingers after the rest of the cold symptoms have resolved can stick around for up to 25 days.

How are cold viruses able to infect the body?

Cold viruses have found clever ways to overcome the immune system’s defenses and cause infection. Understanding how they break past the body’s barriers can help explain why colds are so prevalent:

Rapid mutation: Rhinoviruses mutate quickly, allowing them to evade immune system detection. They are able to alter key proteins on their outer surface that antibodies would recognize.
Respiratory droplet transmission: The viruses spread through tiny respiratory droplets that can easily enter the body through the eyes, nose or mouth.

Replication in cool temperatures: Rhinoviruses replicate best at temperatures around 91°F – the temperature inside the nose. This makes the upper airways the ideal site for multiplication.
Viral load: It’s easy to become exposed to a high dose of cold viruses through close contact with sick individuals. Higher viral loads overcome the immune system faster.
Direct cell infection: Cold viruses can directly infect epithelial cells lining the nasal passages and throat to replicate themselves.

How does the immune system respond?

Although cold viruses manage to sneak past some of the body’s defenses, the immune system still mounts a vigorous response. Here are some of the ways it fights back:

Inflammation: Immune cells release histamines and cytokines that dilate blood vessels and increase inflammation. This leads to symptoms like congestion, runny nose, and malaise.
Mucus production: Goblet cells in the nasal tissues secrete copious mucus that traps and removes viruses and infected cells.

Immune cells: Neutrophils, macrophages, dendritic cells, T-cells and B-cells all activate to detect and clear the virus.
Antibodies: Specialized antibodies called Immunoglobulin A (IgA) neutralize viruses before they can infect cells.
Antiviral interferons: Interferons disrupt viral replication and prevent further spread of infection.

This immune response is what ultimately resolves the cold symptoms, although it takes time to kick into full gear. The inflammation and excess mucus production is what causes the bothersome symptoms during the first week or so of infection.

Are antibiotics helpful for treating colds?

Since colds are caused by viruses, antibiotics are NOT effective for treating them. However, some physicians may prescribe antibiotics if a secondary bacterial infection occurs, such as a sinus infection or ear infection. In this case, antibiotics are appropriate to fight the bacterial pathogen, but they still don’t treat the underlying cold virus. Unfortunately, overuse of antibiotics for viral illnesses has contributed to the development of drug-resistant bacteria.

What complications can arise from colds?

Although colds are generally minor annoyances, they can sometimes lead to more serious complications, especially in those with weakened immune systems. Potential complications include:

Sinusitis: Prolonged inflammation and mucus production can trigger sinus infections. Symptoms include facial pain and green or yellow nasal discharge.
Otitis media: The Eustachian tubes connecting the middle ears to the nasal cavity can swell, allowing viruses or bacteria to become trapped in the ears. This causes ear pain, pressure and headaches.
Asthma flare-ups: The airway inflammation caused by a cold can exacerbate asthma. Coughing, wheezing, chest tightness and shortness of breath may occur.

Bronchitis: Some cases involve airway inflammation extending into the lower lungs, resulting in persistent cough, congestion and fever.
Pneumonia: Secondary bacterial infections or impaired cough reflexes in weakened patients can lead viruses or bacteria to infect the lungs. This causes difficulty breathing, chest pain and fever.

Conclusion

Colds are ubiquitous due to the many viruses that cause them and the ease of transmission through respiratory droplets. While anyone can get infected, those with weakened immune systems, underlying respiratory conditions, or inadequate rest tend to get hit harder. Understanding how these viruses bypass the body’s defenses paints a picture of why they are so common and difficult to prevent. The misery of cold symptoms results from the immune system’s efforts to combat the viral invasion. Knowing the role the inflammatory response plays should discourage the use of inappropriate antibiotics. Instead, get plenty of rest and fluids to allow your immune system to do its job. Most colds resolve on their own within 7-10 days. However, seek medical care if severe or prolonged symptoms emerge to treat any complications promptly.