List of what causes xerostomia and conditions for which xerostomia symptoms are related. If you want to know, "Why do I have xerostomia?" consider that xerostomia can be caused by a number of illnesses. This is a list of diseases that xerostomia is a symptom of, including diseases associated with xerostomia. What diseases cause xerostomia? The list you're viewing contains items like Lichen planus and Dehydration. This list of diseases with xerostomia as a symptom is in alphabetical order with images when available, though it can also be sorted. If you could say "I am experiencing xerostomia," please consult a physician.