Stained pillow-covers are everyone's nightmare, especially using white linen.
To help remind guests they can use tissues provided for them and it safes the hosts lots of hassle and extra work and loss of linen. (yes, it costs a bit - but not everyone showers before bed and I rather pay a bit extra done throwing out my best linen! )
An extra towel could be provided for those using argan oil and related hair products. This is a very rich and creating deep staining marks. Another infamous one is tanning products and hair dye...
Hope this helps you co-hosts.
If you have more ideas, please show us. The more ideas the better.