If your instrument lives in an area where the relative humidity is dry or if you depend on air conditioning or heating to control the temperature in your home/office/studio, (just about everywhere I know of), then your instrument will very likely suffer from the low or constantly changing humidity levels.
The solution is simple and inexpensive. Install a simple, passive humidifier in each of your instruments, while they are not being played. The humidifier will slowly release moisture into the wood of the guitar, uke, mando etc. This slow moisture release will help keep the instrument's wood from drying, cracking, shrinking and expanding.