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.
Stress and anxiety are unexpected factors that can also influence this. When we are under pressure, our sleep patterns change, and this affects how facial muscles relax and how saliva is swallowed. A stressful night can, for example, cause an increase in drooling, making it an indirect indicator of how our body reacts to stress. Even if we don’t notice it while we sleep, our brain is constantly regulating functions to keep us healthy, and drooling can be a side effect of these dynamics.
Although it may seem annoying, drooling serves important functions. Saliva is essential for oral health, protecting teeth, aiding digestion, and keeping the mouth hydrated. The fact that our brain continues to stimulate saliva production throughout the night, even when some leaks, is a sign that our body continues to take care of itself while we sleep. In fact, drooling is a reminder that our bodily functions never stop, even when we’re seemingly “inactive.”
