Waking up to find drool on your pillow can feel a little embarrassing, but it’s actually very common. For many people, it’s simply a normal part of how the body behaves during sleep, particularly during the deeper stages when the body is most relaxed.

As you drift into deep sleep, your muscles begin to loosen throughout the body. This relaxation also affects the muscles that control your jaw and swallowing reflex. When these muscles relax, the mouth may open slightly and the natural swallowing process slows down.

Because swallowing becomes less frequent, saliva can gradually build up in the mouth. When there isn’t enough swallowing to clear it away, the excess saliva may slip out, which leads to drooling during sleep.

Your sleeping position can also influence how likely this is to happen. People who sleep on their side or stomach tend to drool more because gravity allows saliva to flow out of the mouth more easily while they rest.

Sleeping on your back, on the other hand, often reduces drooling. In that position, saliva is more likely to remain in the mouth instead of escaping unnoticed during the night.

Mouth breathing can also play a role, especially if your nose is blocked by allergies, congestion, or illness. In addition, digestive issues such as acid reflux may cause the body to produce extra saliva to protect the throat. While occasional drooling is harmless, sudden changes or difficulty swallowing may be worth discussing with a doctor. In most cases, however, it’s simply a natural result of the body relaxing during sleep.