When and for how long is a cold contagious?

Q. When and for how long is a cold contagious?

A. Your cold may be contagious just before symptoms appear and after they have begun to fade, but the period of highest contagion is when you’re experiencing the strongest symptoms, says Dr. Kimberly Dowdell, a primary care physician at Tufts Medical Center. That’s when the cold virus is at its highest level in your body. Some people will continue to have symptoms such as congestion or a sore throat after they are no longer contagious, but these are often residual symptoms that take a week or two to resolve.

It usually takes between 24 to 72 hours from the time you are first infected by a cold virus for it to multiply and spread enough to give you those first sniffles and throat pains, Dowdell says. The duration of colds varies widely, but most people will have strong symptoms for three to 10 days before they taper off. “There are over 200 viruses that have been associated with the common cold,” she adds, which explains why colds are so variable in duration and intensity.

Colds are usually transmitted by exposure to an infected person’s mucus, either from surface or skin contact (cold viruses can live on skin for three hours and other surfaces up to four hours), or from particles from coughs and sneezes. Saliva, incidentally, does not usually contain high levels of cold viruses. The best prevention is frequent hand-washing and avoiding touching your eyes, mouth, or nose with your hands.