The burning feeling from chili peppers comes from capsaicin, which is concentrated in the white pith.

The longer version

Capsaicin binds to a receptor on sensory nerves that normally responds to heat, so the brain interprets the signal as burning even though no tissue damage is occurring. The compound is produced in the glands of the pale tissue that holds the seeds, which is why that part tastes hottest while the outer flesh is milder.

Seeds themselves are not the source, though they pick up capsaicin from contact. Because the molecule is oily rather than water soluble, water spreads it around while fatty liquids dissolve it more readily. Sensitivity varies a lot between individuals, and repeated exposure tends to blunt the response over time.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.