As humidity increases, moisture content of wood goes up fast, causing it to expand and swell. When high humidity is combined with high temperature, glue joints could possibly become weakened and may even open slightly. Then, for example the glue under the bridge could weaken causing the bridge to pull off. On the contrary, if the moisture content of wood is forced down in a hurry, portions of it shrink faster than others, causing cracks and open joints. For all these reasons, rapid changes in local humidity are what you want to guard your guitar against. In view of that, you can follow the below recommendations:
- Don't let the guitar next to a source of dry heat. (e.g. radiators, heater) since they raise the temperature and drop down the humidity of the surroundings.
- Don't let the guitar exposed to freezing or blistering temperature for a long time, for instance inside a car park outside.
- Avoid hanging your guitar on an outside wall during winter months. The wall will be cooler than the inside air. The result is a conflict between the temperature of the top and back, with potential damage as a result.
- Store your guitar in its case when not in use. Humidity is easier to control in a smaller space. This allows the guitar to acclimate to room temperature more slowly, decreasing the possibility of wood and finish cracks.