Common Cold Overview: Causes, Symptoms, Transmission

The common cold is caused by any of about 200 viruses. Viruses are baffling bundles of genetic material. They’re so tiny that if a human throat cell were the size of the typical house, a cold virus would be about the size of a door or window. Using the common definition of “life,” viruses are barely even alive. Technically, each cold virus causes a “different” cold, but because all colds produce pretty much the same symptoms, we consider the common cold a single illness.

Cold viruses reproduce best in relatively dry air at around 90Ëš F, notes cold researcher Elliott Dick, Ph.D., recently retired chief of the respiratory viruses research laboratory at the University of Wisconsin, at Madison. Your first line of defense is your nose. It warms and moistens incoming air, making it less hospitable to the virus. In addition, your nose and throat are lined with mucus that traps virus particles like flypaper, and microscopic hairs (cilia) that push this mucus down into the stomach, where the acid in your stomach destroys the virus particles. But every so often—one to three times a year for the typical adult, and up to 12 times a year for young children—those pesky virus particles penetrate your throat’s protective mucus, and infect your throat cells.

This may comes as a surprise, but cold viruses don’t cause cold symptoms. Your sore throat, congestion, runny nose, and cough all result from your immune system’s battle against the infection. Before cold-infected throat cells die, they release special chemicals—notably interferon and immunoglobulin A (IgA)—that rally your immune sytstem to arms for the “cold war.” As your immune system swings into action, the tiny blood vessels in your throat expand. This draws extra blood to the infection, bringing with it white blood cells and other immune warriors, notably, antibodies, histamine, and bradykinin. Eventually, your swollen blood vessels trigger local pain nerves, and you feel “a cold throat coming on.” The phrase is ironic, because by the time you develop that sore throat, you’ve already been infected for about 24 hours.”

As the days pass, the extra fluid drawn to your throat to fight the infection accumulates in the sinus cavities around the nose, causing nasal congestion. Some of it leaks out as a runny nose, or triggers sneezing. Finally, your immune system’s fight against the infection irritates the bronchial tubes, and you develop the dry, hacking cough. “You feel fine as you become infected with colds,” says University of Nebraska cold researcher Stephen Rennard, M.D. “You feel ill because your body is making you well.

Young children catch the most colds because their immune systems are not fully developed, and because they are lax in personal hygiene. In addition, Dr. Dick explains, recovery from every cold confers an estimated three to five-year immunity—and possibly longer—to that specific virus and its close relatives, and children have not lived long enough to have developed much of this virus-induced immunity.

Colds spread by either the “aerosol route” or by “direct contact.” Aerosol means through the air. “When you have a cold and cough, sneeze, or just exhale,” Dr. Dick explains, “you spew virus particles into the air. If someone inhales them, bingo, they can catch the cold.”

Direct contact refers to your fingers. “We all touch our noses subconsciously several times an hour,” says cold researcher Jack Gwaltney, a professor at the University of Virginia at Charlottesville. “When you have a cold, nose-touching contaminates your fingers with virus particles. If you touch other peoples’ hands or hard surfaces—counters, doorknobs, telephones, etc.—you deposit virus on them, other people literally pick it up on their fingertips. Then they touch their noses and can get infected.” They might also rub their eyes. The tear ducts in the inner corners of the eyes are connected by a tube to the nasopharynx, so eye-rubbing with cold-contaminated fingertips can also transmit the common cold.

Red Flags and Warnings

Never treat children’s cold with aspirin or aspirin-like herbs. For fevers in children under 18 colds, flu, or chickenpox, do not give aspirin, or its herbal equivalents: willow bark, meadowsweet, or wintergreen. The combination of viral fevers and aspirin is associated with Reye syndrome, a rare, but potentially fatal illness that affects the brain and liver. Instead, place the child in a tepid bath. If you can’t resist medication, give acetaminophen (Tylenol, Panadol, St. Joseph Aspirin-Free, etc.). When in doubt, call your child’s physician.