Finding drool on your pillow when you wake up might feel embarrassing, but it is actually a common and usually harmless part of sleeping. For most people, occasional drooling simply reflects what happens to the body as it relaxes during sleep.

As you drift into deeper sleep, many muscles throughout your body become more relaxed. This includes the muscles involved in controlling your jaw, mouth, and swallowing reflex. As a result, your mouth may open slightly while you are asleep.

At the same time, your swallowing becomes less frequent. Saliva continues to be produced, however, even while you are sleeping. When it accumulates faster than you swallow it, some of the excess can escape through your mouth and end up on your pillow.

Your sleeping position can also make a noticeable difference. People who sleep on their stomachs or sides may be more likely to drool because gravity can encourage saliva to move toward the edge of the mouth.

Sleeping on your back, by contrast, may reduce drooling for some people. In this position, gravity generally helps keep saliva inside the mouth, making it less likely to leak onto your pillow.

Mouth breathing is another common factor. A blocked or stuffy nose caused by allergies, a cold, or congestion can force you to breathe through your mouth, increasing the likelihood that your mouth will remain open during sleep.

Certain conditions, including acid reflux, may also contribute to increased saliva production. Your body can produce extra saliva to help protect and lubricate the throat, which may lead to more noticeable drooling overnight.

Occasional drooling is generally nothing to worry about. However, a sudden and persistent increase, difficulty swallowing, choking during sleep, or other unusual symptoms deserves medical attention. Otherwise, waking up with a little drool is simply a normal consequence of a relaxed body and peaceful sleep.