Exhaust fans are the minimum necessary in houses for taking out stale air. You may have a fan, but it may not be working. It could be clogged up, improperly installed or simply too noisy for anyone to turn it on. Quiet fans, with good controls are a must in our energy efficient and often stuffy houses.
If you want to really have comfort, air quality and economy, you should install a Heat Recovery Ventilator which takes stale air out of the bathroom and kitchen all day long, brings in the same balanced amount of fresh air for the living spaces and uses the heat going out to warm up the cold air coming in. They are great.