In the first few days of a cold, the mucus that comes out of your child’s nose
is clear. This occurs because the virus that is invading your child’s nose and
sinus cavity causes inflammation that stimulates his mucus-producing cells.
After a few days, the body’s immune system begins to attack the virus. When this
happens white blood cells die and become mixed in with the mucus giving it a
yellow or green color.
This progression is part of the natural history of a cold
and does not imply that you child has a bacterial infection. Doctors become
concerned about a bacterial sinusitis when a cold lasts longer that 10 to 14
days or a child is much sicker than one would expect for a typical cold.