Normally we produce around one litre of saliva each day, which is swallowed without even thinking about it. But because swallowing is a motor function, and Parkinson’s causes rigidity and bradykinesia, this spontaneous mechanism can be disrupted as the muscles in the throat, tongue and mouth become more difficult to control. Saliva then builds up in the mouth and, as the muscles which tightly seal the lips also become weaker, the risk of the saliva escaping is increased.
Also the stooped posture that is typical of Parkinson’s, with the head bent forwards and the chin pointing down, can be a contributory factor as this causes saliva to accumulate at the front of the mouth where it can easily dribble out.
