Chili peppers produce a unique sensation of intense heat that is often confused with actual temperature. This feeling of piquancy, or spiciness, is purely a sensory experience resulting from a chemical interaction with the nervous system. The heat felt on the tongue and skin is not a thermal burn, but a neurological response triggered by specific compounds within the pepper. Understanding this phenomenon requires examining the chemical structure and the biological mechanism they exploit.
Capsaicin: The Chemical Culprit
The burning sensation in peppers is caused by a family of compounds called capsaicinoids, with capsaicin being the most abundant and potent member. These molecules are colorless and odorless. Capsaicinoids are not uniformly distributed throughout the pepper fruit; contrary to common belief, the heat does not reside primarily in the seeds.
The highest concentration of these compounds is found in the placental tissue, the white pith or “ribs” that hold the seeds inside the pepper. This inner tissue synthesizes the capsaicinoids, which accumulate on the inner walls. Capsaicin is a hydrophobic molecule, meaning it repels water, so it is not easily washed away or dissolved by water-based liquids.
The Biology of the Burn
The mechanism by which capsaicin creates the sensation of heat involves a protein receptor in the nervous system called Transient Receptor Potential Vanilloid 1, or TRPV1. This receptor is an ion channel found primarily on sensory neurons, which detect pain and temperature changes. The TRPV1 receptor is naturally activated by multiple stimuli, including physical heat above 109°F (43°C) and the presence of certain acids.
When capsaicin enters the mouth, it binds directly to the TRPV1 receptor, mimicking the effect of a damaging thermal stimulus. This binding causes the channel to open, allowing positively charged ions, such as calcium and sodium, to rush into the nerve cell. The influx of ions depolarizes the neuron, generating an electrical signal that is transmitted to the brain. The brain then interprets this signal as a burning sensation.
Measuring Intensity: The Scoville Scale
The intensity of a pepper’s heat is quantified using the Scoville Scale, a measurement system expressed in Scoville Heat Units (SHU). This scale was originally developed in 1912 by pharmacist Wilbur Scoville using an organoleptic test. This method involved extracting the capsaicinoids and diluting them in sugar water until a panel of human tasters could no longer detect any heat; the dilution factor determined the SHU rating.
Today, the heat is measured more accurately and objectively using High-Performance Liquid Chromatography (HPLC). HPLC analyzes the total concentration of all capsaicinoids present, and the results are then converted into standardized Scoville units, providing a precise measure of pungency. For perspective, a bell pepper registers 0 SHU, a jalapeño typically falls between 2,500 and 8,000 SHU, and a ghost pepper can exceed 1,000,000 SHU.
How to Stop the Fire
To effectively relieve the burning sensation, one must use substances that can physically dissolve and remove the capsaicin from the TRPV1 receptors. Since capsaicin is a lipophilic, or fat-soluble, molecule, consuming water offers little relief because it cannot effectively dissolve the compound. Water often just spreads the capsaicin around the mouth, intensifying the burning.
The most effective remedies are those containing fat or oil, as these non-polar substances will bind to the capsaicin and carry it away. Whole milk, yogurt, and ice cream work well due to their fat content. The casein protein in dairy also assists by surrounding and washing away the capsaicin molecules. Consuming starches like bread or rice can provide physical relief by acting as an abrasive to wipe the compound off the nerve endings.