"That bed hasn't been aired, love."

This exchange from *Noises Off * confuses me a bit.

I’m unclear on the purpose of airing a bed, and how a hot water bottle would accomplish the same task. Is it just that in an old house, a bed that has sat undisturbed would be chilly, unless the bedding was turned back and exposed to the room’s heat? That’s the only thing I can think of.

Can anyone enlighten me?

Total guess, but perhaps because an unaired bed might be damp? My grandmother still thinks that sleeping in a damp bed causes sickness.