What causes a sensation of drooling on the left side of the mouth?

Reviewed by Yoshinori Abe, MD

Internal Medicine

One-sided drooling occurs when nerves or muscles on that side of your mouth cannot control saliva as effectively as the other side. This asymmetry is often linked to neurological conditions such as Parkinson's disease, stroke, or Bell's palsy, but it can also result from dental issues, sleep position, or nasal congestion forcing mouth breathing.

Because one-sided drooling can signal anything from a minor irritation to a serious neurological concern, identifying the underlying cause quickly matters. A free, instant, online symptom check can help you understand possible causes based on your specific symptoms and guide you toward the right next steps—whether that's a visit to your dentist, primary care doctor, or a neurologist.

Reviewed for medical accuracy: 07/15/2026

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Explanation

Your body normally controls saliva using nerves and muscles that work together when you swallow. Sometimes, these nerves or muscles may not work evenly on both sides of your mouth. This imbalance can make your left side feel like it is drooling more.

In neurological conditions e.g. Parkinson's disease, changes in brain function can affect the signals that tell your muscles how to move. This disruption can mean that the muscles on one side might not move saliva to the back of your mouth as effectively, so it feels like you have extra saliva or drooling.

Also, if the salivary glands on that side produce a bit more fluid, or if there is any disruption in the normal swallowing process, you may notice more saliva on that side. If this sensation is uncomfortable or causes trouble with eating or speaking, you can use a free AI symptom checker to help identify potential causes and determine whether you should seek medical attention.

(References)

Polychronis S, Nasios G, Dardiotis E, Messinis L, Pagano G. Pathophysiology and Symptomatology of Drooling in Parkinson's Disease. Healthcare (Basel). 2022 Mar 11;10(3):516. doi: 10.3390/healthcare10030516. PMID: 35326994; PMCID: PMC8951596.
Iorgulescu G. Saliva between normal and pathological. Important factors in determining systemic and oral health. J Med Life. 2009 Jul-Sep;2(3):303-7. PMID: 20112475; PMCID: PMC5052503.
Huang T, Tang LL, Zhao JY, Shang SA, Chen YC, Tian YY, Zhang YD. Drooling disrupts the brain functional connectivity network in Parkinson's disease. CNS Neurosci Ther. 2023 Oct;29(10):3094-3107. doi: 10.1111/cns.14251. Epub 2023 May 5. PMID: 37144606; PMCID: PMC10493659.

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