Sneezing, scratchy throat, runny nose—everyone knows the first signs of a cold, probably the most common illness known. Although the common cold is usually mild, with symptoms lasting 1 to 2 weeks, it is a leading cause of doctor visits and missed days from school and work. According to the Centers for Disease Control and Prevention, 22 million school days are lost annually in the United States due to the common cold. In the course of a year, people in the United States suffer 1 billion colds, according to some estimates. Children have about 6 to 10 colds a year. One important reason why colds are so common in children is because they are often in close contact with each other in daycare centers and schools. In families with children in school, the number of colds per child can be as high as 12 a year. Adults average about 2 to 4 colds a year, although the range varies widely. Women, especially those aged 20 to 30 years, have more colds than men, possibly because of their closer contact with children. On average, people older than 60 have fewer than one cold a year. In the United States, most colds occur during the fall and winter. Beginning in late August or early September, the rate of colds increases slowly for a few weeks and remains high until March or April, when it declines. The seasonal variation may relate to the opening of schools and to cold weather, which prompt people to spend more time indoors and increase the chances that viruses will spread to you from someone else. Seasonal changes in relative humidity also may affect the prevalence of colds. The most common cold-causing viruses survive better when humidity is low—the colder months of the year. Cold weather also may make the inside lining of your nose drier and more vulnerable to viral infection.

Colds are highly contagious and spread through touching contaminated surfaces, coughing, or sneezing. Treatment is aimed at reducing the symptoms. And since there are so many viruses that cause the cold, it is unlikely that there will ever be a vaccine to protect people from "catching" a cold.

Handwashing is the single most effective way to reduce the spread of infections such as the common cold. It is also wise to stay away from people who have a cold, especially during the first three days of the infection. If you have a cold, cover your nose and mouth when you cough or sneeze and wash your hands frequently.

Symptoms of the common cold usually begin 2 to 3 days after infection and often include
-- Mucus buildup in your nose
-- Difficulty breathing through your nose
-- Swelling of your sinuses
-- Sneezing
-- Sore throat
-- Cough
-- Headache
-- Fever is usually slight but can climb to 102 degrees Fahrenheit in infants and young children.

Cold symptoms can last from 2 to 14 days, but like most people, you’ll probably recover in a week. If symptoms occur often or last much longer than 2 weeks, you might have an allergy rather than a cold. Colds occasionally can lead to bacterial infections of your middle ear or sinuses, requiring treatment with antibiotics. High fever, significantly swollen glands, severe sinus pain, and a cough that produces mucus, may indicate a complication or more serious illness requiring a visit to your healthcare provider.

Source: National Institutes of Health; National Institute of Allergy and Infectious Diseases

For a comparison of Common Cold vs. Flu symptoms, click here .