Dry mouth, also known as xerostomia, can be caused by a variety of factors. Here are some common causes of dry mouth:

1. Medications: Many medications can cause dry mouth as a side effect. Some common medications that can cause dry mouth include antihistamines, decongestants, antidepressants, blood pressure medications, and muscle relaxants.

2. Medical conditions: Certain medical conditions can cause dry mouth, including diabetes, Sjogren's syndrome, HIV/AIDS, Parkinson's disease, and stroke.

3. Radiation therapy: Radiation therapy to the head and neck area can damage the salivary glands and cause dry mouth.

4. Nerve damage: Nerve damage in the head and neck area can affect the salivary glands and cause dry mouth.

5. Dehydration: Not drinking enough fluids can cause dry mouth.

6. Mouth breathing: Breathing through the mouth instead of the nose can cause dry mouth.

7. Tobacco use: Smoking or chewing tobacco can cause dry mouth.

8. Aging: Saliva production tends to decrease as we age, which can lead to dry mouth.

Dry mouth can be a temporary or chronic condition, depending on the underlying cause. If you are experiencing dry mouth, it's important to talk to your dentist or healthcare provider to determine the underlying cause and develop a treatment plan.