If you wake up with a wet pillow, it may just be a normal effect of sleeping on your stomach or your side. In some cases, however, it could be a sign of a more serious problem.
Saliva coats your mouth and throat, makes it easier to swallow, helps food taste better, and keeps the area clean by washing away leftover food particles. Normally, you produce less saliva while you sleep than during waking hours. In fact, the flow of saliva all but stops during sleep. If you have a problem in your mouth or throat, however, your body may respond by producing more saliva. Sinus congestion, acid reflux, seizure disorders, dental infections, and other physical disorders can also result in excess saliva flowing out of your mouth or, perhaps worse, down your throat or windpipe.
You may have excess saliva in your mouth due to a medical condition such as gastroesophageal reflux, or gastrointestinal reflux disease (GERD), that causes fluid to back up into your esophagus, especially when you are lying down. In this case, your body produces extra saliva in an attempt to neutralize the stomach acids that are backing up. You may dribble onto your pillow, but that's the least of it. You may also experience fluid drainage that flows back into your airways and causes you to wake up coughing and choking during the night. To prevent this type of excess saliva production, you must treat the underlying condition.
The flow of saliva is controlled by your autonomic nervous system, and involves muscles in your face and neck. Any condition that impairs swallowing or causes disruptions in the nervous system, or damage to muscles in your head and neck, can cause drooling. That is why people with Parkinson's disease or Lou Gehrig's Disease (also known as amyotrophic lateral sclerosis, or ALS), for example, may experience excessive and uncontrollable drooling, day and night.
Excess drooling due to neurological problems is often controlled with medication to prevent aspiration, or breathing in of excess fluids or food. These medicines include anti-cholinergic drugs that target the nervous system and botulism toxin, or Botox, which targets the muscles. Extreme cases are sometimes treated with radiation targeted at the salivary glands.
But not all drooling signals a problem. Sometimes a wet pillow simply means your mouth fell open when you fell asleep and some saliva escaped. That's usually due to your sleeping position. A simple solution is to prop up your pillows so you sleep on your back with your head upright. If that doesn't solve the problem, speak with your doctor or dentist to determine whether or not you have a more serious condition that is causing you to drool and what steps you can take next.
Sources:
Colorado State University: Salivary Glands and Saliva
http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/salivary.html
Columbia University College of Dental Medicine: Salivary glands: Saliva and Gastro-esophageal Reflux
http://dental.columbia.edu/hospital_dentistry/oms/salivary008.html
Drexel University College of Medicine: Drooling
http://www.drexelmed.edu/home/HealthEncyclopediaArticles/Symptoms/Drooling.html
