Spitting is the forceful expulsion of saliva and other contents from the mouth. Although often viewed as a social taboo, this common human action serves fundamental biological and behavioral purposes. The act of spitting is a mechanism rooted in physiology, protection, and conscious choice, not merely a vulgar habit. Understanding why people expel oral contents requires examining the material being expelled and the diverse triggers, from involuntary reflexes to complex social behaviors.
The Function and Composition of Saliva
Saliva, the primary material expelled during spitting, is a watery fluid produced by the salivary glands, consisting of about 99% water. The remaining one percent contains a complex mixture of proteins, electrolytes, and organic molecules. These components include digestive enzymes, such as amylase, which begins the breakdown of starches, and antimicrobial agents like lysozyme and antibodies for immune defense.
The fluid serves a constant lubricating function, protecting the delicate mucosal tissues of the mouth from drying out and injury during speaking or chewing. Saliva also acts as a buffer due to its bicarbonate and phosphate content, helping to neutralize acids produced by bacteria and foods. This buffering action is important for maintaining oral health and preventing tooth demineralization. The body produces approximately one to one and a half liters of saliva daily, necessitating either swallowing or, under certain conditions, expulsion.
Reflexive and Protective Expulsion
Many instances of spitting are involuntary reflexes designed to safeguard the body’s digestive and respiratory systems. A primary function is the protective expulsion of irritants or harmful substances from the mouth. If a person accidentally ingests something bitter, toxic, or unexpectedly hot, the immediate gag reflex can forcefully eject the material before it is swallowed.
Another common physiological trigger is the need to clear the respiratory tract of excess mucus or phlegm. Conditions like post-nasal drip or a respiratory infection lead to the accumulation of thick, sticky secretions. While most saliva is swallowed, thick mucus is often difficult to ingest, making expectoration a more efficient way to clear the airways and prevent aspiration into the lungs.
Voluntary Spitting in Context
Beyond protective reflexes, many spitting instances are conscious and intentional, driven by temporary discomfort or behavioral factors. People often spit to clear the mouth of residual tastes or chemical irritants, such as strong mints, tobacco residue, or a sudden unpleasant taste. This intentional act manages the immediate oral environment when swallowing the contents is undesirable.
The context of intense physical activity, particularly in sports, frequently leads to voluntary spitting. During heavy exertion, athletes breathe rapidly through the mouth, causing the water component of saliva to evaporate quickly. This leaves behind a thicker, stickier mucus, often rich in the protein MUC5B, which can feel uncomfortable and impede breathing. Spitting is the preferred method of clearance because swallowing this thick mucus can interrupt the rhythmic breathing required for performance.
On a behavioral level, spitting can serve as a non-verbal social cue, expressing disdain, disgust, or aggression. Historically, the act has also been linked to superstitious beliefs, such as a light spitting gesture to ward off the “evil eye” or bad luck. These conscious acts highlight the versatility of spitting as a form of physiological management and communication.
Medical Conditions Causing Excessive Spitting
When spitting becomes excessive, it is often related to a medical condition known as sialorrhea or ptyalism. This results from two primary issues: the overproduction of saliva (hypersalivation) or the inability to effectively clear and swallow normal amounts. Excessive production can be a side effect of certain medications, particularly antipsychotic drugs like clozapine and risperidone, which stimulate salivary glands.
Gastroesophageal reflux disease (GERD) can also trigger waterbrash, where stomach acid irritation causes a reflex increase in saliva production. More commonly, excessive spitting is a consequence of impaired neuromuscular control, which makes swallowing difficult. Neurological conditions such as Parkinson’s disease, cerebral palsy, and stroke can weaken the oral and facial muscles necessary for managing secretions, leading to a buildup of saliva that must be expelled. If a person experiences a sudden, unexplained increase in saliva production or difficulty managing oral secretions, a consultation with a healthcare provider is appropriate.