Dehydration: This is often the most common cause of acute mouth dryness, resulting from insufficient fluid intake, excessive sweating, or other factors leading to a loss of body fluids.

Medication side effects (e.g., anticholinergics, antidepressants, antihistamines): Many medications can cause dry mouth as a side effect by reducing saliva production.
Anxiety or stress: Stress and anxiety can lead to mouth breathing and decreased saliva production, resulting in dryness.
Breathing through the mouth: Instead of breathing through the nose, mouth breathing can dry out the mouth.
Sjögren's syndrome: An autoimmune disorder that can cause dryness in the eyes, mouth, and other parts of the body, though it's less common than other causes.

Diabetes: Uncontrolled diabetes can lead to dry mouth due to high blood sugar levels causing dehydration.
Sarcoidosis: A condition where inflammatory cells form in various parts of the body, including the salivary glands, which can lead to dry mouth.
HIV/AIDS: Certain infections and medications associated with HIV/AIDS can cause dry mouth.
Tuberculosis: Though rare, TB can affect the salivary glands and cause dry mouth.

Amyloidosis: A condition where abnormal proteins (amyloid) accumulate in organs and tissues, potentially affecting salivary glands.
Ectodermal dysplasias: A group of disorders identified by the lack or impairment of the ectodermal structures and their accessor organs such as hair, nails, teeth, skin, and other glands, including salivary glands.
Irradiation of the head and neck: Radiation therapy in this area can damage salivary glands, leading to chronic dry mouth, but this would typically be a known part of a patient's medical history.
Graft-versus-host disease (GVHD): A complication that can occur after a stem cell or bone marrow transplant, where the newly transplanted material attacks the recipient's body, potentially affecting the salivary glands.