Is smoking old cigarettes bad for you?

They get stale.

Cigarette tobacco has an ideal moisture content after it's cured. They're wrapped in a preservative foil and packaged in light cardboard packages with cellophane wrapped around each pack in order to preserve the moisture content from point of manufacture to point of sale. Once the cellophane wrapping is removed, the cigarettes will slowly begin to dry out. This isn't noticeable during the normal consumption of a pack by the end user. When most of the moisture has leached out of the cigarettes, they will taste stale, and burn away rapidly.