Throat numbing sprays, often containing ingredients like benzocaine or phenol, are widely used for the temporary relief of sore throat pain. While these products do not function as traditional cough medicines, they may offer a temporary, indirect benefit against a persistent cough. Understanding the body’s natural defense mechanism is the first step in determining the spray’s efficacy.
The Mechanism of the Cough Reflex
The act of coughing is a rapid, protective reflex designed to clear the airways of irritants and foreign materials. This physiological process begins when sensory receptors lining the respiratory tract detect irritation. These receptors, which include rapidly adapting receptors (RARs) and C-fibers, are highly concentrated in the larynx, trachea, and larger bronchi.
When stimulated by triggers like post-nasal drip, mucus, or inflammation, these receptors send an electrical impulse. This signal travels along the vagus nerve to the cough center located in the medulla oblongata of the brainstem. The central nervous system then initiates the motor pathway, triggering the coordinated, forceful muscle contractions that result in a cough.
How Numbing Sprays Provide Local Relief
Numbing throat sprays contain active ingredients like benzocaine, a local anesthetic. Benzocaine works by diffusing into the membranes of local nerve endings. Once inside the nerve cell, the molecule binds to voltage-gated sodium channels.
This binding action prevents the channels from opening, which blocks the influx of sodium ions necessary to generate an action potential. Phenol, another common ingredient, functions similarly as an oral analgesic to deaden the sensation of pain and discomfort in the throat tissues. The numbing effect is fast-acting, highly localized to the area of application, and temporary in duration.
The Indirect Effect on Cough Frequency
Throat numbing sprays do not affect the cough center in the brain, meaning they are not central antitussives. However, the localized anesthetic action can have a significant indirect effect on certain types of coughs. By desensitizing the peripheral sensory receptors, specifically the RARs in the pharynx and upper larynx, the spray can reduce the number of irritation signals sent to the brain’s cough center.
This effect is most noticeable for coughs that originate from a “tickle” or irritation high in the throat, such as those caused by pharyngitis or chronic post-nasal drip. Some studies involving local anesthetics like lidocaine spray have demonstrated a reduction in cough frequency. The relief is short-lived.
When to Choose a True Cough Suppressant
When the cough is not merely due to localized throat irritation, a true antitussive is necessary. These medications act centrally, directly elevating the threshold for coughing in the brain’s cough center. True cough suppressants, such as Dextromethorphan (DM) and codeine, are designed for this purpose.
Dextromethorphan is a common non-opioid suppressant that inhibits the cough reflex. Codeine, an opioid derivative, also suppresses cough by acting on the central nervous system. These central-acting drugs are typically reserved for dry, non-productive coughs that interfere with sleep or daily function. Suppressing a productive or “wet” cough is generally avoided, as the cough reflex is needed to clear mucus and secretions from the lower airways.