How long is a cold contagious?

What the evidence says

Colds are caused by viruses, and the Canadian Paediatric Society explains that colds usually last about a week but can continue for as long as two weeks. The contagious window is shorter than the illness itself: MedlinePlus notes that people are most contagious for the first 2 to 3 days of a cold, and a cold is most often not contagious after the first week. Timing matters here too.

Symptoms typically start 2 to 3 days after exposure to the virus, which means a child (or adult) can pass on a cold before anyone realizes they're sick. Since more than 200 different viruses can cause colds, and young children haven't built immunity to most of them, it's common for kids to seem to catch one cold after another all winter. For child care or school, Canadian guidance is fairly relaxed about colds specifically: CPS materials note a child with a common cold does not need to be excluded from child care unless they are too unwell to take part in normal activities.

The main practical takeaways are to expect the first few days to be the highest-risk period for spreading it, and to use good hand hygiene and covering coughs/sneezes throughout the illness, since low-level shedding can continue a bit longer. If symptoms are unusually severe, don't improve after 7 to 10 days, or your child is having trouble breathing, it's worth checking in with your doctor, since these could point to a different illness such as flu or a bacterial complication.