Sjögren's Syndrome: This autoimmune disorder is the most common cause of chronic dry eyes (xerophthalmia) and dry mouth (xerostomia), characterized by lymphocytic infiltration of the lacrimal and salivary glands.

Aging: As people age, the production of tears and saliva can decrease, leading to dry eyes and mouth.
Medication Side Effects: Certain medications, such as antihistamines, decongestants, and antidepressants, can cause dry eyes and mouth as a side effect.
Environmental Factors: Prolonged exposure to dry environments, wind, or smoke can contribute to dry eyes and mouth.
Hormonal Changes: Hormonal fluctuations during menopause or pregnancy can lead to changes in tear and saliva production.

Lymphoma: Sjögren's syndrome increases the risk of developing lymphoma, which can present with symptoms similar to those of Sjögren's.
Sarcoidosis: This autoimmune disorder can cause dry eyes and mouth, as well as other systemic symptoms, and can be life-threatening if not treated.
HIV/AIDS: Dry eyes and mouth can be symptoms of HIV/AIDS, particularly in the later stages of the disease.

Graft-Versus-Host Disease (GVHD): This condition can occur after bone marrow or stem cell transplantation and can cause dry eyes and mouth, among other symptoms.
Hemochromatosis: This genetic disorder can cause dry eyes and mouth, as well as other systemic symptoms, due to iron overload.
Amyloidosis: This condition can cause dry eyes and mouth, as well as other systemic symptoms, due to the deposition of abnormal proteins in various tissues.