Short Answer: Purchase a hygrometer to monitor the relative humidity in your home.  

Expanded Answer: Always use your home ventilation system such as the bathroom fan, to control moisture. Regular use of your home ventilation system will exhaust excess airborne moisture caused by bathing and showering. In the summer, you may need to dehumidify to avoid moisture damage to your cabinets. In the winter, lower humidity levels may cause wood to shrink ( such as door panels ) so you may need the use of a humidifier to add moisture back into the air.

Relative humidity levels should not exceed 60%.