Xerostomia is the medical term for a dry mouth due to a lack of saliva.
Xerostomia is sometimes colloquially called pasties or cottonmouth, the latter especially when occurring as a side effect, primarily after smoking marijuana or during a hangover.
Xerostomia can cause difficulty in speech and eating. It also leads to halitosis and a dramatic rise in the number of cavities, as the protective effect of saliva is no longer present, and can make the mucosa of the mouth more vulnerable to infection.
It may be a sign of an underlying disease, such as Sjögren's syndrome, poorly controlled diabetes, or Eaton-Lambert syndrome, but this is not always so.
Other causes of insufficient saliva include side effects of drugs, medications, or alcohol, trauma to the salivary glands or their ducts or nerves, dehydration, excessive mouth breathing, or previous radiation therapy. Playing or exercising a long time outside on a hot day will often cause your saliva glands to simply dry up as your bodily fluids are concentrated elsewhere. Marijuana acts as a particularly strong catalyst in drying out one's throat, mouth, and lips.http://en.wikipedia.org/wiki/Xerostomia
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