That damp patch on your pillow is usually a quiet sign that your body has slipped into deeper, more restorative sleep. As you drift down into those stages, the muscles in your face, jaw, and throat naturally loosen. Your mouth may fall slightly open, your swallowing reflex slows, and saliva that would normally be swallowed simply pools and escapes. For side and stomach sleepers, gravity makes this even more likely, gently pulling that saliva out of the corner of your mouth.

Other everyday factors add to the effect. If your nose is blocked from a cold, allergies, or chronic congestion, you’re more likely to breathe through your mouth, drying it out and changing how saliva moves. Acid reflux can prompt your body to create extra saliva to protect your throat, some of which may leak out at night. Most of the time, this is harmless and normal. But if drooling suddenly worsens, comes with trouble swallowing, or feels drastically different, it’s worth speaking with a doctor. Otherwise, that wet pillow is usually just evidence of a body fully at rest.