Drooling during sleep is common and usually harmless. It often happens during deep REM sleep when muscles relax, causing the mouth to open and saliva to escape instead of being swallowed.

Sleeping position plays a big role—side and stomach sleepers are more likely to drool due to gravity, while back sleepers tend to swallow saliva more easily, reducing drooling.

Nasal congestion from allergies, colds, or sinus infections can force mouth breathing, increasing saliva flow. In some cases, drooling may be linked to conditions like acid reflux, sleep apnea, or neurological disorders.

Occasional drooling isn’t a concern, but frequent or excessive drooling—especially with other symptoms—may require medical attention. Simple changes like adjusting sleep position or treating allergies can often reduce the issue.