What Causes Symptoms of the Common Cold?

What causes the common cold and the miserable symptoms that result when you become infected? A tiny virus and your own immune system in overdrive are to blame.

Does Zinc Help Fight the Common Cold?

There are many different groups of viruses that can cause the common cold, but human rhinoviruses (HRVs) are responsible for causing the majority, and even within this one group, there are hundreds of different varieties. Rhinoviruses are tiny (even among microbes), belonging to the family Picornaviridae, which translates as small (pico) RNA (rna) viruses (viridae).

What Is a Virus?

To understand how the rhinovirus infects and causes illness, it helps to first know what viruses actually are. Unlike bacteria and other cellular pathogens, viruses are not even alive. That is why antibiotics, medications used to fight bacterial infections, are of no use in treating a viral infection such as a cold. Viruses are acellular infectious particles that are strictly parasitic, unable to reproduce without the help of an unwitting host.

A virus' single goal is to make more copies of itself. It does this by invading the living cells of a host. In the case of rhinoviruses, those living host cells are in the human nasal cavity, and as soon as the viruses invade those cells the game's on.

How You Catch a Cold

A person can become infected with the Rhinovirus by breathing it in aerosolized particles, such as when an infected person coughs or sneezes or when a person touches a surface that is infected and then touches his or her nose.

Rhinoviruses are highly infective. Just one viral particle is enough to cause a cold in half of the people who become infected. And the human nasal passage is the ideal place for Rhinoviruses to set up shop. This virus requires temperatures a little below our normal core body temperature in order to reproduce, and the cells of the nose and upper throat, nearer the outside of the body and exposed to cool air, are lower in temperature.

Cold Symptoms Are Caused by Your Immune System

Once a person is infected, the first symptoms usually occur within 12 hours and peak between one and three days after infection. Once your body catches on and recognizes that there is an infection, cells in the infected area release histamines, which dilate blood vessels in the infected area. This is part of the body's response, initiating acute inflammation that helps to quickly transport white blood cells to the site of infection.

There is often a local swelling caused by blood vessels leaking plasma in the area of infection. Mucous membranes in the nasal passages also begin to secrete fluid. This is what causes the runny nose, watery eyes, congestion and sinus headache. The chemical signaling and response of the body's immune system can also stimulate nerve fibers, resulting in aches and pains and triggering sneezing and coughing reflexes.

How to Avoid Catching a Cold

The best way to avoid catching a cold is to:

• avoid being in the direct path of the coughs and sneezes of those infected
• wash your hands and use hand sanitizer at regular intervals
• avoid touching your nose and eyes, particularly if you hands haven't been recently washed

Still, most of even the most careful people do catch colds. Having a strong immune system is the next best defense, and that results from taking good care of your body, getting exercise, eating right and keeping those vices under reasonable control.

Sources

Bauman, R. (2004). Microbiology. Pearson Benjamin Cummings.

McCoy, L. (2004). "Rhinovirus: An Unstoppable Cause of the Common Cold." Science Creative Quarterly.

For more information on infectious disease, see the Virtual Microbiology Classroom. To learn about the use of zinc in reducing the symtpms and length of cold infections, see the Suite101 article "Does Zinc Help Fight the Common Cold?"

This article is not intended to be used for the diagnosis or treatment of illness. If you believe that you are ill, see a doctor, not a computer.