How Spicy Heat Works: The Science of Capsaicin and Piperine
Spicy is not technically a taste. It is a pain response. Understanding the chemistry behind it explains why some people tolerate chilli heat easily, why dairy relieves it but water does not, and why spicy foods can paradoxically cause pleasure.
Capsaicin: The Active Compound in Chillies
Capsaicin binds to TRPV1 receptors — the same receptors that detect physical heat above 43°C. When capsaicin activates these receptors, your brain receives a signal that something hot is touching you, even though the tissue temperature has not changed. The burning sensation is a neurological response, not chemical damage. This is why capsaicin is used in topical pain relief products — repeated application desensitises the TRPV1 receptor over time.
The Scoville Scale
Heat in chillies is measured in Scoville Heat Units (SHU), originally determined by dilution testing and now measured by HPLC chromatography. Bell peppers score 0. Jalapeños range 2,500 to 8,000 SHU. Habaneros hit 100,000 to 350,000. The Carolina Reaper, currently one of the hottest documented chillies, peaks above 2 million SHU. Pure capsaicin itself is around 16 million SHU.
Why Milk Works and Water Does Not
Capsaicin is fat-soluble and non-polar. Water is polar and cannot dissolve it — drinking water spreads capsaicin around your mouth rather than removing it. Milk contains casein, a protein that acts as a detergent and binds to capsaicin molecules, carrying them away. Full-fat milk works better than skimmed. Bread, rice, and starchy foods also absorb capsaicin through adsorption.
The Endorphin Response and Spice Tolerance
The pain signals from capsaicin trigger endorphin release — the same mechanism behind runner’s high. This is why habitual chilli eaters report genuine pleasure from heat that non-habitual eaters find painful. Tolerance builds through repeated exposure as TRPV1 receptors desensitise. Regular chilli consumption has also been associated in epidemiological studies with reduced all-cause mortality, though the mechanism is not fully established.
