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How the Body Fights Off Cold and Flu

Cold and flu are the most common human ailments. The average adult suffers through two or three colds per year, and children can get two to three times that many.1 The term "cold" is just an umbrella expression for hundreds of similarly behaving viruses—a host of pathogens so vast that doctors diagnose more or less exclusively by symptom, if they diagnose at all. By the time a doctor figured out which virus was responsible, your cold would be gone.

Given the challenge, it's no wonder we don't have a cure for the common cold. Instead, we make do with our own immune systems. Cold and flu viruses both change their makeup continually, so our bodies need time to recognize the "new" virus as a threat and prepare an adequate defense. When our immune systems take too long to respond, or when the virus is especially aggressive, we get sick.

Strictly speaking, viruses are not even alive. They are more than a thousand times smaller than bacteria and are little more than a strip of genetic material with a protein coating. Upon entering the body, they attach themselves to human cells and force the host cells to produce virus DNA. When the host cells eventually burst, new viruses spill out and attack new, healthy cells.2 Once a critical mass of these cells has been damaged, the immune system swings into action and begins sending out virus-fighting cells and proteins, which can cause inflammation and, in the case of the flu, high fever. Most of the symptoms we experience are the result of our bodies trying to fight the infection, rather than the infection itself.

Making Sense of the Signs

One of the first signs we usually notice is congestion from the excess of green or yellow mucus our bodies produce (to trap the offending viruses). The color does not indicate whether you have a bacterial infection or viral infection. It could be either. It's merely a sign of infection, caused by an enzyme found in white blood cells.3

The muscle soreness you notice, especially in bouts of the flu, is also a product of your body's immune response. It's working overtime to fight the infection and pulls protein from your muscles in service of the cause. Adding extra protein to your diet can help alleviate that soreness.3

And be sure to keep smiling, even when you’re feeling down: Researchers have found that a positive attitude and social interaction strengthen the immune system and make illness less likely.

1 Understanding the Symptoms of the Common Cold and Influenza. The Lancet Infect Dis.
2 Apex Learning Science. Are Viruses Alive?
3 Short Sharp Science. Eight Cold Facts. New Scientist blog.