The frequent need for smokers to spit is a direct consequence of the body’s physiological defense systems reacting to inhaled tobacco smoke components. This behavior is a necessary response to chemical irritants and toxins entering the mouth and respiratory tract. The process involves two distinct mechanisms: a rapid chemical signal that increases watery saliva production, and a sustained response that drastically increases thick mucus output in the lungs. Both reactions force the smoker to expel the resulting fluids.
Nicotine and the Salivary Reflex
The initial cause of excessive, watery saliva production, known as hypersalivation, is a direct chemical reaction triggered by nicotine itself. Nicotine acts as a cholinergic agonist, mimicking the function of the neurotransmitter acetylcholine. This chemical interaction stimulates the parasympathetic nervous system, which controls involuntary body functions, including salivation.
When nicotine activates receptors near the salivary glands, it prompts the release of signaling chemicals. This cascade dramatically increases the output from the major salivary glands (parotid, sublingual, and submandibular). The immediate result is a flood of thin, liquid saliva designed to dilute and wash away the foreign, irritating chemical compounds entering the mouth.
Smoke Irritation and Mucus Overproduction
The chronic need to spit is primarily due to the profound irritation of the respiratory system caused by the thousands of chemicals in tobacco smoke. When inhaled, these toxic compounds cause inflammation along the lining of the trachea and bronchi. In response, the respiratory tract drastically increases the production of sticky, thick mucus, often called phlegm.
This overproduction is driven by the hyperproliferation of specialized goblet cells, which secrete mucus. As the number of these cells increases, the volume of mucus secreted into the airways rises significantly. The purpose of this thick, viscous material is to trap fine particulate matter and toxins from the smoke, preventing them from penetrating deeper into the lung tissue.
Concurrently, the toxic components of the smoke paralyze and damage the cilia, the microscopic hair-like structures that line the airways. Normally, these cilia move the mucus layer upward and out of the lungs, a process called mucociliary clearance. With the cilia immobilized, the massive volume of thick mucus remains trapped. The smoker must use forceful coughing to clear this accumulated phlegm, bringing the smoke-laden material up into the throat and mouth, necessitating spitting.
Why Swallowing is Avoided
Once the body produces this combination of watery saliva and thick phlegm, swallowing the material is highly undesirable. The excess fluid from hypersalivation is saturated with chemical byproducts from the smoke, giving it an unpalatable and acrid taste. Sensory perception alone makes swallowing the substance a repulsive experience.
The phlegm brought up from the lungs is chemically tainted, extremely thick, and voluminous. Attempting to swallow this dense material can easily trigger a gag reflex or induce nausea. Smokers also recognize that the expelled material contains trapped toxins and particulate matter, leading to a decision to spit it out rather than allow it to travel into the digestive system.