Humidity is a factor acoustic guitar manufacturers take very seriously, and for good reason. A poorly humidified guitar can develop such problems as bad string action, fret buzzing, cracking in the wood or binding, protruding fret ends and so on. The correct conditions in which to store a guitar is between 45% and 55%, and this is best monitored using a hydrometer. The case offers the best protection against overly dry or damp air, but even then, it is recommended to store the guitar with a product such as a Humidipak to help maintain correct levels of water vapour in the guitar and the case.
A quick check over the guitar by a qualified tech will identify if there are any humidity problems. On a dry guitar, symptoms include; low/buzzing action, hump on the fretboard where it meets the body, sunken top, possibly with a crack running vertically down the centre, back of the guitar looks unusually flat and sharp fret ends. Symptoms of a wet or damp guitar will be; high action, unusually swollen top/back, unusual warping and recessed fret ends.
These symptoms are usually completely reversible with no lasting damage to the guitar, but regular checking can prevent something more serious.
Until next time, TECH care of yourselves and your guitars.