Nerve Damage

• An injury to the head or neck or surgery that has caused nerve damage in those areas can cause dry-mouth symptoms.
  
  

Tobacco Use

• Chewing tobacco or smoking can lead to xerostomia in part because lesser levels of saliva are produced, according to the Universidad del Pais Vasco in Spain.
  
  

Cancer Therapy

• Cancer treatments can damage salivary glands when radiation to the neck and head is involved. Damaged glands produce less saliva, which results in a dry, tough-feeling mouth.
  
  

Medications

• According to the Mayo Clinic, the most common cause of xerostomia is medication side effects. Hundreds of medications list dry mouth as a possible side effect.
  
  

Health Conditions

• Parkinson's disease, depression and Sjogren's syndrome, among others, may cause dry-mouth symptoms. Some sufferers of diseases such as Alzheimer's may believe they have dry mouth even though tests show salivary glands producing at normal levels.