What Your Brain Says When You Drool in Your Sleep
When you wake up and notice your pillow is damp, the first thing that usually comes to mind is a feeling of embarrassment or discomfort. However, drooling while sleeping is much more common than we think. It’s not a sign of carelessness or poor hygiene, but rather a reflection of what’s happening inside our body, and more specifically, our brain, while we rest.
Although it may seem trivial, this phenomenon reveals fascinating details about how our bodily functions work while we sleep and how our body maintains balance without us even realizing it.
Nighttime drooling, medically known as nocturnal sialorrhea, occurs when saliva production exceeds the mouth’s capacity to contain it. During the day, we swallow constantly, and our brain carefully regulates the amount of saliva we produce.
At night, however, this dynamic changes. The muscles of the mouth and face relax deeply during sleep, and this relaxation makes it easier for saliva to escape without us having any control over it. Furthermore, our sleeping position has a major impact. Sleeping on your stomach, for example, causes gravity to favor saliva flow, while sleeping on your side can also favor it depending on the tilt of your head.
The brain doesn’t stop while we sleep; in fact, it’s very active, alternating between different sleep phases: REM and non-REM.
During REM sleep, which is the phase in which most vivid dreams occur, the body’s muscles relax even more, and although saliva production may decrease, the risk of saliva leakage increases due to the extreme relaxation of the mouth muscles. This combination makes drooling during this phase quite common and often unavoidable. The brain, although aware of internal saliva signals, cannot intervene during deep sleep, so saliva leakage occurs silently.
There are physical and health factors that can cause some people to drool more than others. Nasal congestion is a classic example: when we have difficulty breathing through the nose, the body tends to breathe through the mouth, and this causes saliva to leak more easily. Similarly, certain medications and medical conditions that affect saliva production, swallowing, or muscle coordination can also increase the likelihood of drooling.
Even habits such as smoking or consuming alcohol before bed can disrupt natural saliva production or affect how facial muscles handle swallowing during the night.
Diet and hydration also play an important role. Eating very salty, spicy, or very sweet foods before bed stimulates saliva production. On the other hand, dehydration causes saliva to thicken, making it difficult to swallow and causing it to accumulate in the mouth and eventually leak. Our brain, although it detects these signals, cannot act on them while we sleep, so the result is a silent leak of saliva. This explains why some days we wake up with a completely wet pillow and other days we don’t, even if we sleep in the same position.
Drooling also has a curious relationship with the development of the jaw and teeth, especially in children. Children tend to drool more while sleeping because their mouths have not yet fully developed the coordination necessary to swallow saliva during sleep. In adults, dental alignment issues, dentures, or even natural tooth wear can contribute to this phenomenon. Thus, drooling is not simply an accident; it is a reflection of the biological functioning of our mouth and brain.