A:

Researchers have identified over 200 different viruses that that cause the common cold. The biggest offender is the rhinovirus. It causes up to 40% of colds.

So that makes it hard to speak of the common cold as one specific illness. Rather, it is a collection of symptoms that are easy for doctors and patients alike to recognize:

• Runny nose
• Sneezing
• Nasal congestion
• Sore throat

Cold symptoms typically start one to two days after exposure. They usually last for about 4 to 9 days. Then they go away without specific treatment.

People are most contagious (most likely to pass the cold onto others) during the first 24 hours they have symptoms. But they will remain infectious for as long as the symptoms persist.

How long a person is contagious depends on the type of virus that caused the cold. For example, rhinovirus may be found in respiratory secretions for several weeks. But people with this cold virus infection are most contagious for the first 4 days of symptoms.

Other viruses, such as the coronavirus (a less frequent cause of the common cold) are shed only during the first 2 to 4 days that symptoms are present. You will never know which virus caused your cold. So it makes the most sense to follow these steps:

• Wash your hands frequently.
• Carefully discard any used tissues while you have cold symptoms.
• Be aware that the virus may still be present in your respiratory secretions for a few weeks. Even after your cold symptoms have gone away.