A: It is indeed possible for the humidity to be too high. If there is too much moisture in the air, acoustic guitars and other light wooden instruments are most at risk. The wood can swell to the point that glue joints break and/or cracks develop. High humidity can also result in the instrument’s top bowing up, which will raise the action and put a lot of stress on the bracing and body seams.
A hygrometer is your friend! Most experts recommend keeping the humidity in the 40-50% range.