It's not unusual for toothbrush makers to recommend changing your toothbrush if you've got a cold, but as Slate's Julia Felsenthal points out, that's almost always nonsense.
In fact, as most of us are well aware, you're extremely unlikely to be re-infected by a virus—like a cold—once you've already had it, since you've now got antibodies to fend off whatever germs are still sticking around. The exception: When it's somebody else's toothbrush (naturally) or when you've been sick with a bacterial infection:
If you were afflicted with strep throat, for example, a colony of streptococcal bacteria might end up on your toothbrush and remain there long enough to give you a second case after you'd taken a course of penicillin. But that threat might be mitigated by toothpaste, which sometimes contains antibacterial compounds. And, despite the claims of toothbrush manufacturers, this wouldn't apply to a typical case of the (viral) sniffles.
Anyway, a good reminder: Despite what your toothbrush packaging may say, you probably don't need to run out and buy a new toothbrush just because you were sick. Photo by Ellie.