People drool when they sleep because they have difficulty swallowing saliva or retaining it while they are sleeping. In people with excess saliva production or drooling problems while awake, drooling while asleep can become a significant problem. There are some health concerns associated with excessive drooling that lead some people to pursue treatment to address the issue. Treatment can be provided by a general practitioner, neurologist, and other medical specialists, depending on the underlying cause.

The salivary glands are in continuous production, generating saliva to lubricate the mouth. Saliva production increases when people eat. The mouth is designed to help people retain saliva and people regularly swallow to allow the saliva to drain into the stomach so it can be eliminated from the body. While asleep, the mechanisms for keeping saliva in the mouth and swallowing it may not function as well; swallowing reflexes, for example, can be less active during sleep.

In babies, drool during sleep is very common because the reflexes involved have not formed and been refined yet. In adults, some drooling is normal, but excessive amounts can be a sign of an underlying medical problem. People with certain neurological disorders can have difficulty managing their drool while sleeping or awake. Parkinson's disease, cerebral palsy, stroke, facial paralysis, and Alzheimer's disease can all be associated with drool during sleep. Pregnant women can also start producing more saliva than usual.

People may also find that they experience drooling while sleeping when they are not feeling well. For these individuals, there may be a spike in drool production associated with a period of ill health, followed by a reduction. Certain medications can also increase saliva production and lead to drooling that becomes more noticeable during sleep. If people notice that they appear to be producing more saliva than usual or that they have trouble retaining it, they may want to bring it up with a physician to discuss possible causes and treatment options.

In addition to soiling bedclothes, drooling can become a problem because people may be at risk for inhaling the fluid or developing other problems. There are some medications that can sometimes address a drool problem. In addition, patients sometimes benefit from physical therapy to develop stronger reflexes. Such therapy can also help people with speech and eating if they are experiencing difficulties. Surgery on the salivary glands can be another option, although it is usually a treatment of last resort.