Waking up with some drool on your pillow can feel embarrassing, but it is common and usually harmless. During deeper sleep, the muscles that control your jaw, mouth, and swallowing relax, which can allow your mouth to open slightly while you are resting.

At the same time, your body continues producing saliva even though you swallow less frequently during sleep. If saliva builds up faster than you swallow it, some can escape through your mouth. Sleeping on your side or stomach may make this more noticeable because gravity can encourage saliva to move toward the edge of your mouth.

Mouth breathing can also contribute to nighttime drooling, especially when a cold, allergies, or nasal congestion makes it difficult to breathe through your nose. Certain conditions, such as acid reflux, may increase saliva production as the body works to protect and lubricate the throat.

Occasional drooling is generally nothing to be concerned about. However, a sudden or persistent increase, difficulty swallowing, choking during sleep, or other unusual symptoms may warrant medical attention. Otherwise, a little drool on the pillow is often simply a sign that your body was relaxed and sleeping peacefully.