You know the drill. Your throat feels scratchy, you start sneezing and coughing, and pretty soon you're in the grip of a nasty cold. To add insult to injury, all that big-time misery is from a tiny invader -- a living thing called a virus.
And it's not just one you need to dodge. There are more than 200 that can lay you low.
What is it about swine flu that has people so nervous? Should seniors in particular be worried? To learn more, WebMD went to medical experts and got their answers to these and other questions about the 2009 H1N1 virus.
There are also a lot of viruses that doctors haven't identified. About 20%-30% of colds in adults are caused by these "unknown" bugs.
How and When They Strike
Cold viruses have a lot in common, but each type has its own style, too.
Rhinovirus. This bunch is most active in early fall, spring, and summer. They cause 10%-40% of colds. You'll feel plenty miserable when you catch one, but the good news is they rarely make you seriously sick.
Coronavirus. These tend to do their dirty work in the winter and early spring. The coronavirus is the cause of about 20% of colds. There are more than 30 kinds, but only three or four affect people.
RSV and parainfluenza. These viruses cause 20% of colds. They sometimes lead to severe infections, like pneumonia, in young children.
What's Not Causing Your Cold
Time to set the record straight. There's no evidence that you get sick because you've been out in cold weather. And don't worry if you got overheated. It doesn't lead to a cold either.
Another myth says your diet is the cause. Don't pay attention to that tall tale. And ignore someone who says you're getting sick because your tonsils or adenoids are large.
On the other hand, research suggests that stress and allergies that affect your nose or throat may raise your chances of getting infected by a cold virus.
Other Causes of the Common Cold
About 10% to 15% of adult colds are caused by viruses also responsible for other, more severe respiratory illnesses.
The causes of 20%-30% of adult colds, presumed to be viral, remain unidentified. The same viruses that produce colds in adults appear to cause colds in children. The relative importance of various viruses in children's colds, however, is unclear because it's difficult to isolate the precise cause of symptoms in studies of children with colds.
There is no evidence that you can get a cold from exposure to cold weather or from getting chilled or overheated.