What causes a common cold?

The cold is a common infection of the upper respiratory tract. Although many people think you can catch a cold by not dressing warmly enough in the winter and being exposed to chilly weather, it’s a myth. The real culprit is one of more than 200 viruses.

The common cold is spread when you inhale virus particles from an infected person’s sneeze, cough, speech, or loose particles from when they wipe their nose. You can also pick up the virus by touching a contaminated surface that an infected individual has touched. Common areas include doorknobs, telephones, children’s toys, and towels. Rhinoviruses (which cause the most colds) can live for up to three hours on hard surfaces and hands.

Most viruses can be classified into one of several groups. These groups include:

  • human rhinoviruses
  • coronaviruses
  • parainfluenza viruses
  • adenoviruses

Some other common cold culprits have been singled out, such as the respiratory syncytial virus. Still others have yet to be identified by modern science.

In the United States, colds are more common in the fall and winter. This is mostly due to factors such as the start of the school year and the tendency for people to remain indoors. Inside, air tends to be drier. Dry air dries up the nasal passages, which can lead to infection. Humidity levels also tend to be lower in colder weather. Cold viruses are better able to survive in low humidity conditions.

This group of viruses — of which there are more than 100 types — is by far the most common identified cause of colds. The viruses grow best at the temperature inside the human nose.

Human rhinoviruses (HRVs) are highly contagious. However, they rarely lead to serious health consequences.

Recent research has found that HRVs manipulate genes and it is this manipulation that brings about an overblown immune response. The response causes some of the most troublesome cold symptoms. This information could lead scientists to important breakthroughs in the treatment of the common cold.

There are many varieties of coronavirus that affect animals, and up to six can affect humans. This type of virus typically causes mild to moderate upper SARS (severe acute respiratory syndrome).

Other viruses that may cause a cold include:

  • human parainfluenza virus (HPIV)
  • adenovirus
  • respiratory syncytial virus (RSV)

These three groups of viruses typically lead to mild infections in adults, but may cause severe lower respiratory tract infections in children, older adults, and those with weakened immune systems. Premature babies, children with asthma, and those with lung or heart conditions are at greater risk for developing complications such as bronchitis and pneumonia.

One strand of HPIV called HPIV-1 causes croup in children. Croup is characterized by the loud, startling sound that is produced when the infected individual coughs. Crowded living conditions and stress increase the risk of respiratory disease. For instance, the CDC found that military recruits are at greater risk for contracting adenoviruses that develop into respiratory illnesses.

The common cold will usually run its course without complication. In some instances it may spread to your chest, sinuses, or ears. The infection can then lead to other conditions such as:

Ear infection: The main symptoms are earaches or a yellow or green discharge from the nose. This is more common in children.

Sinusitis: It occurs when a cold does not go away and stays for long periods of time. Symptoms include inflamed and infected sinuses.

Asthma: Breathing difficulty and/or wheezing that can be triggered by a simple cold.

Chest infection: Infections can lead to pneumonia and bronchitis. Symptoms include lingering cough, shortness of breath, and coughing up mucus.

Strep throat: Strep is an infection of the throat. Symptoms include a severe sore throat and sometimes a cough.

For colds that do not go away, seeing a doctor is necessary. It’s important to seek medical attention if you have a fever higher than 101.3°F, a returning fever, trouble breathing, persistent sore throat, sinus pain, or headaches.

Children should be taken to the doctor for fevers of 100.4°F or higher, if they have cold symptoms for more than three weeks, or if any of their symptoms become severe.

There is no set cure for the cold, but combining remedies may alleviate symptoms.

Over-the-counter cold medicines usually combine painkillers with decongestants. Some are available individually. These include:

  • Pain relievers such as aspirin and ibuprofen are good for headaches, joint pain, and fever reduction.
  • Decongestant nasal sprays such as Afrin, Sinex, and Nasacort can help clear the nose cavity.
  • Cough syrups help with persistent coughs and sore throats. Some examples are Robitussin, Mucinex, and Dimetapp.

Alternative medicine

Alternative medicine is not proven to be as effective at treating colds as the above methods. Some people do find relief in trying it.

Zinc can be used most effectively if taken 24 hours after the first symptoms. Vitamin C, or foods rich with it (like citrus fruits), are said to boost the immune system. And echinacea is often thought to provide the same immune system boost.

Home remedies

During a cold, it is suggested that you get extra rest and try to eat a low-fat, high-fiber diet. You should also drink a lot of liquids. Other tips for home care:

  • The warmth and liquid of chicken soup can help sooth symptoms and congestion.
  • Gargling with salt water may relieve a sore throat.
  • Cough drops or menthol candies can help with sore throats and cough. The candies provide a coating over the throat that soothes inflammation.
  • Controlling your home’s temperature and humidity can prevent the growth of bacteria.

Read more: Is it a cold or the flu? »