People can be infected with the common cold virus at anytime of the year, but most Americans “catch” colds in the fall and winter. Scientists believe the higher number of infections during the colder months may be caused by people remaining indoors. This puts people in closer contact for longer periods of time during the winter.

While this may be true, researchers at the National Institute of Health (NIH) may have found another reason that has to do more with the virus itself. In March 2008, the NIH scientists discovered that the outer coating of the influenza virus (the virus that causes the flu) toughens up in cooler temperatures. They believe that this stronger outer coating, called the envelope, helps the virus survive longer outside the human body. If the virus can live longer outside a human host, it can linger around long enough to infect another person. Scientists are not sure yet if the envelope on the virus that causes the common cold also gets stronger in colder weather, but they think this may explain why people catch more colds in the wintertime.

This microscopic image shows the bacteria that can cause tuberculosis.

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