When a small amount of wasabi—or its common substitute, horseradish paste—is consumed, it delivers a unique, instantaneous, and sharp burning sensation that often shoots directly up into the nasal passages. This intense feeling is distinctly different from the lingering, deep heat of a chili pepper. The immediate, volatile nature of the sting is a protective response triggered by a specific chemical compound that activates specific sensory nerves.
The Chemical Culprit
The fiery sensation is caused by a chemical compound known as Allyl Isothiocyanate (AITC), which is found in wasabi, horseradish, and mustard plants. AITC is not naturally present as an active compound in the intact wasabi root; instead, it is stored in the form of precursor compounds called glucosinolates. The production of AITC only begins when the wasabi rhizome is grated, chewed, or otherwise damaged, which breaks down the cell walls.
This cellular damage allows the glucosinolates to mix with a specific enzyme called myrosinase, which then rapidly hydrolyzes the precursors to generate the active Allyl Isothiocyanate. This is a fundamental difference from the heat in chili peppers, which is caused by the non-volatile oil capsaicin.
The Sensory Nerve Reaction
Once created, AITC acts as a potent irritant by directly activating specific pain-sensing nerve endings in your mouth and nose. The key player in this biological reaction is a specialized protein channel called TRPA1 (Transient Receptor Potential Ankyrin 1). This channel is often referred to as the “wasabi receptor” because of its high sensitivity to AITC.
When AITC molecules bind to the TRPA1 channels, they physically cause the channel to open, allowing an influx of ions like calcium into the nerve cell. This sudden flow of ions generates an electrical signal that the nervous system interprets as a noxious irritant, pain, or extreme cold. The TRPA1 receptor serves as a general detector for a broad class of volatile, reactive environmental irritants.
Why the Sensation Travels Upward
The reason the burn bypasses the tongue and travels specifically to the nose and sinuses is due to the unique physical properties of Allyl Isothiocyanate. AITC is highly volatile, meaning it converts into a gas very easily and rapidly, especially when exposed to body temperature inside the mouth. This gaseous AITC then quickly travels upward through the back of the throat and into the nasal cavity via the retro-nasal passage.
This pathway is lined with the same sensitive mucous membranes and TRPA1 receptors that were activated initially in the mouth. Since the volatile gas is inhaled directly into the sinuses, it concentrates the irritant effect in the nasal passages, creating the characteristic “clearing” sensation.
Stopping the Burning Sensation
Since the sensation is caused by a volatile gas, the most effective relief methods focus on removing the gaseous AITC from the nasal passages. The burn is typically short-lived, often subsiding within a few minutes because the compound evaporates quickly. Breathing deeply through the mouth and exhaling through the mouth helps to redirect the vapors away from the sensitive TRPA1 receptors in the nose.
Drinking milk can also provide relief, as AITC is slightly soluble in organic solvents and milk contains fats and the protein casein that may help bind to the compound. However, simply waiting for the highly volatile chemical to dissipate is usually the quickest way to end the intense, transient discomfort.