Head-mounted display (HMD) devices need cleaning from time to time for better performance and hygienic concerns.
HoloLens devices need periodic light cleaning. Please refer to Microsoft's guidance on this.
In our experience at GigXR, some customer institutions also find it helpful to make pre-moistened wipes available to users sharing headsets. Users can then remove makeup or sweat from their forehead area before donning the device. If the foam brow pad gets particularly soiled over time, that is an easily replaceable part available from Microsoft or 3rd party vendors.
Each HoloLens comes with a very nice microfiber cloth. Look for it when unpacking the center storage compartment in the case. Don't throw it away! This cloth is perfect for keeping the visor clean on the inside and the camera lenses clean on the outside.
Finally, some GigXR customers have found that systems using UV light to facilitate decontamination are helpful. These do not do the same job as a wipe with a microfiber cloth in terms of removing smudges and greasy residues, however they may offer additional peace of mind in terms of pathogen reduction.