Sushi Eaters Should Not Count on Wasabi to Clear the Nose

Wasabi, (Wasabia japonica) is commonly known as the Japanese horseradish used to enhance the enjoyment of sushi. This spice is a member of the Cruciferae family of plants; its rhizome, the creeping underground stem, is ground into a green paste and used as a condiment. Oral ingestion of wasabi causes a transient burning sensation in the nose, and there is a widely held notion that this produces a decongestant effect. This conclusion is anecdotal, because there have been no scientific studies to prove this concept.

The pungent ingredient in wasabi that causes the nasal burning sensation is allyl isothiocyanate, a chemical also found in mustard and horseradish. The toxicity of allyl isothiocyanate is low, and it is not considered a human carcinogen. It has been produced commercially for more than 60 years.

While there is a subjective improvement in nasal breathing after eating wasabi, knowledge of an objective decongestant effect may have some clinical utility. For example, wasabi may be useful in treating congested patients with hypertension or heart disease, in whom traditional adrenergic decongestants would not be the best regimen. Also, some patients may prefer herbal remedies to traditional western medicines. A temporary decongestant may also have some use if administered before a nasal saline irrigation to improve the lavage.

A new study examined whether oral ingestion of wasabi has both a subjective and objective decongestant effect on the nose. The authors of “The Wasabi Effect” are The David S. Cameron MD, and Raul M. Cruz MD, both from the Department of Head and Neck Surgery, Kaiser Permanente Medical Center, Oakland, CA. Their findings are being presented on September 21, 2004, at the American Academy of Otolaryngology-Head and Neck Surgery Foundation Annual Meeting & OTO EXPO, being held September 19-22, 2004, at the Jacob Javits Convention Center, New York City, NY.

Methodology: This research was performed using the Visual Analog Scale (VAS), a validated instrument that has been used in numerous studies to quantify subjective opening of the nasal passages. Acoustic Rhinometry was used to objectively measure the nasal airway. In this technique, reflected sound waves are analyzed to calculate the nasal cross-sectional area at any distance into the nose, allowing also for calculation of nasal volume. The advantages of acoustic rhinometry are that it is a painless, noninvasive technique that can be rapidly performed and is highly reproducible.

Twenty-two volunteer subjects were used for the study, (12 males, and 10 females, ages 27-68). Subjects were excluded from the study if they had active rhinitis, any recent viral illness (within one week), had prior nasal surgery or significantly abnormal nasal anatomy (e.g. marked septal deviation), or were taking any decongestant or antihistamine medications. None reported allergy to wasabi, mustard, or horseradish.

They were seated and asked to fill out a VAS to subjectively measure their level of congestion, rhinorrhea, itch, and nasal comfort. This consisted of a 100mm horizontal line representing a spectrum between two extremes. The subjects were instructed to mark a single vertical line though the horizontal line rating the subjective nasal sensation at that present time. The distance to this mark was measured from the left side of the scale in millimeters. Congestion was measured by a VAS between “totally clear” and “totally blocked”. Rhinorrhea was measured by a VAS between “not runny” and “very runny”. Nasal itch was measured by a VAS between “not itchy” and “very itchy”. Finally nasal comfort was measured by a VAS between “totally comfortable” and “worst pain imaginable.”

The subjects were then asked to blow their nose, clearing any secretions, after which acoustic rhinometry was performed to objectively measure nasal volume and minimal cross-sectional area. The subjects were then asked to place 0.1 ml of wasabi paste on their anterior tongue and asked to dissolve it in their mouth while breathing through their nose and mouth. This wasabi dose was repeated three times at one-minute intervals. One minute after the last dose of wasabi, the subjects were again asked to blow their noses, and the VAS and acoustic rhinometry measurements were repeated. The subject’s tolerance of this wasabi challenge was also assessed by a questionnaire where subjects rated the experience as “intolerable,” “unpleasant,” “tolerable,” or “enjoyable.”

Results: Oral ingestion of wasabi had no effect on the subjective sensation of nasal comfort, itch, or rhinorrhea. There was a trend towards a sensation of increased nasal patency, as measured by the VAS. However, the acoustic rhinometry data showed that there was a statistically significant congesting effect as measure by total MCA and nasal volume. Seven subjects rated this wasabi test as “unpleasant.” Eleven rated it as “tolerable.” Four rated it as “enjoyable.” None found it “intolerable.”

Conclusions: The researchers believe that the sensation of nasal patency can be attributed to a body of evidence that implicates thermoreceptors in the nasal vestibule and nasal mucosa as an important mediator of this sensation. The theory is that nasal airflow cools these receptors through both evaporative and convective mechanisms. These thermoreceptors send signals to the brain via the trigeminal nerve. The trigeminal nerve is known to convey afferent somatosensory information from the nose including cooling, warming, burning, stinging, itching, tickling, pain, and the perception of humidity. Allylisothiocyanate directly stimulates these trigeminal nerve fibers.

Another theory to explain our results may be the action of the dilator naris muscle. This muscle is responsible for nasal flaring, and its activation has been shown to decrease nasal resistance to airflow in humans by 30 percent, as it stabilizes the nasal valve area. If wasabi activates this muscle, nasal airflow may be facilitated despite an increase in mucosal congestion.

What is known is that oral intake of wasabi is well tolerated. While there is a trend towards a subjective increase in the sensation of nasal airflow, and certainly a widely held misconception by the general public that eating wasabi decongests the nose, it actually congests the nasal mucosa. Essentially, this dichotomy between perception and reality remains speculative, but could involve activation of nasal sensory nerves, and or the dilator naris muscle.