45%-55% relative humidity is optimum. If this is obtained, you minimize the risk of damage.
Temperature and humidity can have a large impact on your guitar’s tuning. Too much or too little moisture will warp the thin wood of your guitar, making it difficult to tune. Eventually, inappropriate levels of humidity will lead to cracks or may even cause the instrument to break or snap.
The optimum level of humidity for a guitar is between 45% and 55%. Generally, dry air poses a more frequent and damaging risk to the instrument. When the humidity drops below the optimum range, the wood of your guitar beings to bleed moisture, leading to shrinkage and cracking. If your guitar has been exposed to excessive humidity seams may separate, bridges may become loose and the action may become unplayable.
1) Use a guitar humidifier when in dry conditions .
2) Keep the guitar in its case when it’s not in use. Never store a guitar by a fireplace, heater, oven, radiator, in a car, or in direct sunlight. These will dry-out and prematurely age any guitar.
3) Care: Wipe down your guitar with a soft cloth after use, and polish it every month or so. Using a very soft cloth and guitar or guitar polish will ensure your instrument maintains its natural oils. Cleaning removes sweat and dust, both of which work to corrode an instrument’s polish and wood, increasing the likelihood that the guitar will dry out. Use products that are designed for the specific parts and materials of your guitar