What's normal: Five or six a year is average; eight to 10 is in the normal range.
What's not: A cold with a fever that lasts more than five days; difficulty breathing (beyond a stuffy nose); a cold that lasts more than 10 days.
Why your child may be vulnerable: Since there are more than 100 viruses that trigger the common cold, it's no wonder young kids fall prey to continual rounds of sniffles, sneezes, and coughs, says Preeti Jaggi, MD, an infectious disease specialist at Children's Memorial Hospital, in Chicago. Plus, if your child is in daycare, he'll be exposed to more of these nasty cold bugs at an earlier age.
Some cold-prone kids may also have a genetically active immune system that reacts more strongly to viruses. Still others may have an immune system that's been coddled by a hyperclean home.
"That's the hygiene hypothesis," says Dr. Kimberlin. "Children's immune systems are designed to learn from exposure to all sorts of things. But researchers increasingly believe that our modern environment may be too clean. As a result, kids aren't building the immunity needed to resist certain illnesses."
Kids with upper respiratory allergies may also get more colds than normal, he adds. The reason? An inflammation of the upper respiratory system can make a child more susceptible to cold germs, or make cold symptoms more pronounced.
Some endless rounds of runny noses may simply be a case of bad timing: Newborns inherit short-term common-cold immunity from their mom, but it wears off after about six months. This leaves summer-born babies without protection just as the winter sneeze season kicks into gear.
Advice for parents: Make sure kids get lots of sleep. If they're eating solid foods, include plenty of fruits and veggies in their diet. In adults, low levels of vitamin C have been linked to harsher colds.
Also, don't smoke in the house, or even better, try to quit. Exposure to secondhand smoke -- even the burnt-tobacco by-products that cling to clothing and furniture -- irritates airways and dulls immunity, raising the risk of a child's cold becoming something worse. For instance, secondhand smoke exposure is responsible for 150,000 to 300,000 cases of bronchitis and pneumonia each year in kids up to 18 months of age.