OK. Now I have your attention. These are some of the consequences of incorrect humidity or temperature extremes, particularly for the more expensive, solid wood instruments. Very little attention has been given to this problem in this country, which is strange considering the extremes of temperature and humidity we have here.

The best relative humidity level for instruments is between 45% and 55%. Most good quality acoustic guitars with solid tops are built under strictly controlled relative humidity in this range.

Low Humidity
 If your guitar's environment (its case or the room) gets below 40% relative humidity (at 24°C) it's going to start "shrinking". To avoid this, simply buy yourself one of the myriad guitar humidifiers (see pic on left), wet it, wring it out, and insert it into the sound-hole of your guitar. It will need to be filled up every few days to keep your guitar healthy and happy. These are best used when the guitar is in its case.

Excess Humidity
With warmer weather the relative humidity of the air can become quite high. When the relative humidity exceeds 60% (at 24°C), the guitar will begin to expand. Silica gel packs, which come in many guitars, are as a desiccant. Store one or two of these inside your case if you live in a humid area.

Extreme Temperature
Problems most commonly happen when you have your guitar outside in extreme cold or hot weather, then enter a room or building with a totally different extreme. The solution to this problem is prevention.  Try not to expose your guitar to extreme temperatures. Failing this, allow your guitar to acclimatise gradually with the case closed for a while (between half and one hour) before opening. Never leave your guitar in the boot or backseat of your car. Temperatures as high as are generated there will cause the glue joints to loosen. and when the instrument cools down again it may be permanently reset in a different position.

Bright Sunlight
If your guitar is exposed to bright sunlight for a period of time, yellowing of the top will occur. This yellowing is not in itself a problem, but if there is some obstruction, such as your arm or the guitar strap laying across the guitar, it will leave a lighter are in the finish.

In an Ideal World...

• Consider keeping one room at a safe humidity level and temperature and keep your guitars in there. It may be easier to maintain, especially in a large house.
• Find a hygrometer to measure the relative humidity level in your room. It will give a rough estimate of the humidity.
• Keep the humidity between 45% and 55%.
• Watch your instrument, it will tell you when it is particularly wet or dry.
• Keep your guitars in their cases when not in use. The case will help keep the guitar's natural moisture in place. Also, if you need to control the moisture content, a case holds a smaller volume of air than a room.
• Don't store your guitar near a direct source of heat, in direct sunlight, or near outside doors.
• If you find that your home is very dry, use a room humidifier to raise the moisture level and keep it there. You may find one beneficial for your health as well.
• Use a guitar humidifier to add moisture to your guitar on a regular basis.  They'll help keep your guitar at a better humidity level, even if your entire house isn't.