Your experience of sudden sweating, flushing, or a runny nose after eating mustard or similar pungent foods is a common biological reaction. This phenomenon is a type of physiological response known generally as gustatory sweating. It is triggered not by actual heat, but by the chemical irritants present in the food itself. Your body interprets the sensation caused by these compounds as a threat, activating defense mechanisms intended to cool you down or flush the irritant away. This physical response is a normal function of the nervous system.
Identifying the Irritant: Allyl Isothiocyanate
The specific compound responsible for the pungent sensation in mustard, wasabi, and horseradish is Allyl Isothiocyanate (AITC). This molecule is not stored in its active form within the plant; rather, it is a defensive agent created upon damage to the plant tissue. Before the mustard seed is processed, AITC exists as a stable precursor compound called sinigrin, which is a type of glucosinolate.
The enzyme myrosinase is stored in a separate compartment from sinigrin within the plant cells. When the mustard seed is crushed, ground, or chewed, water is introduced, and the sinigrin and myrosinase mix together. This enzymatic reaction rapidly hydrolyzes sinigrin, producing the volatile, irritating molecule, Allyl Isothiocyanate. This process explains why dry mustard powder is inert until moisture is added.
The Nervous System Trigger
The physical discomfort, including sweating, begins when Allyl Isothiocyanate interacts with specific sensory receptors in your mouth and nasal passages. AITC is known to bind to a type of protein receptor called the Transient Receptor Potential Ankyrin 1 (TRPA1) channel. This channel is often colloquially referred to as the “wasabi receptor” and is primarily responsible for detecting environmental irritants, cold, and mechanical pain.
The binding of AITC to the TRPA1 receptor involves a covalent modification of specific cysteine residues within the channel. This chemical change forces the ion channel to open, allowing a rush of calcium ions into the nerve cell. This influx of ions generates an electrical signal that the brain interprets as a sudden, intense irritant, similar to extreme cold or a chemical burn.
The brain, receiving this signal of pain and irritation, immediately activates the autonomic nervous system to initiate protective responses. This system controls involuntary actions, and its response here is to attempt to neutralize the perceived threat. Sweating is triggered as a cooling mechanism to regulate the body temperature. The flushing of the skin is due to vasodilation, an expansion of blood vessels that also contributes to body cooling.
Gustatory Sweating and Related Reactions
The sweating you experience is a localized manifestation of gustatory sweating, which is a normal, temporary response of the nervous system to certain chemical stimuli. This particular reaction is directly linked to the activation of the TRPA1 receptor by isothiocyanates like AITC. The immediate and localized nature of the reaction is a distinguishing feature.
This mechanism is different from the sensation caused by chili peppers, which contain the compound capsaicin. Capsaicin primarily activates the TRPV1 receptor, often called the “heat receptor,” which responds to actual high temperatures above 43 degrees Celsius. While both mustard and chili create a sensation of heat and can cause sweating, they achieve this through different molecular pathways.
Other common symptoms alongside sweating include rhinorrhea, or a runny nose, and tearing. The volatile nature of AITC means its gas easily travels up into the nasal cavity, irritating the mucous membranes and triggering an inflammatory response. The body’s defense is to produce excess mucus and tears to dilute and flush the irritant away from the sensitive tissues. This entire collection of symptoms is a protective action, not an allergy or intolerance.