People are hygroscopic meaning that they can take on and give up moisture to the surrounding environment. If a patient is unfortunate enough to be in hospital or a care home for sometime a low humidity environment can result in dehydration.
Typically 40 -60%rh is required to create a comfortable environment for the patient. This can be extended to the operating theatre where low humidity can result in static and the risk of ignition of medical gases and reliability of electronic medical equipment.
Correctly controlled humidity has also been shown to ensure that bacteria are not air bourn which allows them to be removed and eliminated by surface cleaning.