Waking up with a wet pillow can feel embarrassing, but drooling during sleep is far more common—and usually far more normal—than most people realize. In most cases, it’s not a sign of anything serious. Instead, it’s a simple result of how the body behaves during different sleep stages.
Drooling, or excessive saliva leaking from the mouth during sleep, happens when the muscles that control swallowing and keeping the mouth closed become more relaxed than usual. During deeper stages of sleep, especially REM sleep, the body reduces muscle activity significantly. That includes the jaw and facial muscles, which can allow the mouth to fall slightly open.
When the mouth is open and swallowing slows down, saliva naturally collects and may escape from the lips instead of being swallowed.
Common reasons it happens
One of the most frequent causes is simply sleep position. People who sleep on their side or stomach are more likely to drool because gravity allows saliva to exit the mouth more easily. Back sleeping can sometimes reduce this, though it isn’t always comfortable for everyone.
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