Drooling during sleep usually happens because saliva is not being swallowed as often, not because your body is making too much of it. When you fall asleep, the muscles of the face and mouth relax, swallowing slows down, and saliva can pool and leak out, especially if your mouth is open or you sleep on your side.
During deeper stages of sleep, swallowing becomes much less frequent. At the same time, saliva production continues at a lower level to keep the mouth and throat moist. If swallowing pauses for longer stretches, saliva can build up and escape, which is why drooling is more noticeable at night than during the day.
Sleeping position plays a role. Lying on your side or stomach lets gravity pull saliva toward the lips. Mouth breathing from nasal congestion, allergies, or blocked nasal passages also makes drooling more likely because saliva can escape more easily when the lips are open.
Occasional drooling is usually harmless. If it happens often, is new, or comes with trouble swallowing, snoring, or breathing pauses during sleep, it’s important to get checked. A primary care doctor can help decide if a sleep specialist, ENT doctor, or neurologist should be involved. Avoid self-medicating for drooling without medical advice.