Capsaicin comes from chili peppers, specifically fruits of the Capsicum genus. It’s the compound responsible for the burning sensation when you bite into a hot pepper, and it’s produced inside the fruit itself, not in the seeds as many people assume. Pure capsaicin registers 16 million Scoville Heat Units, making it the benchmark against which all pepper heat is measured.
The Plant Behind the Burn
Every chili pepper that brings heat to your food belongs to the Capsicum genus, a group of flowering plants in the nightshade family. The most commonly cultivated species is Capsicum annuum, which includes jalapeños, cayennes, serranos, and bell peppers. Other heat-producing species include Capsicum chinense (habaneros, ghost peppers, Carolina Reapers), Capsicum frutescens (tabasco peppers), and Capsicum baccatum (ají peppers).
Bell peppers belong to the same species as jalapeños, yet they produce zero heat. The difference comes down to a single gene locus called Pun1. When a pepper plant carries two copies of a nonfunctional version of this gene, it cannot produce capsaicin at all. A tiny four-base-pair deletion in the DNA is enough to shut down the entire heat-producing pathway, which is why bell peppers and some other sweet varieties exist.
Where in the Pepper It’s Made
If you’ve ever scraped the seeds out of a jalapeño hoping to reduce the heat, you were on the right track but aiming at the wrong part. Capsaicin is synthesized in the placenta, the white, spongy tissue that runs down the center of the pepper and holds the seeds in place. The compound accumulates in tiny storage compartments within the surface cells of this tissue.
Seeds themselves don’t produce capsaicin. They taste hot only because they sit in direct contact with the placenta and absorb some of the compound. The outer wall of the pepper (the pericarp) can also pick up capsaicin that migrates outward from the placenta, but the concentration is always highest at the source. This is why removing the white ribs and placental tissue is the most effective way to dial down a pepper’s heat when cooking.
How the Plant Builds Capsaicin
Capsaicin is assembled from two separate ingredient streams inside the plant, then joined together in a final step. One stream starts with phenylalanine, an amino acid, and runs through a series of chemical conversions that ultimately produce a compound called vanillylamine. This is related to vanillin, the molecule that gives vanilla its flavor, which is why capsaicin’s full chemical name includes “vanillyl.”
The second stream builds a fatty acid chain. The plant constructs this piece through its normal fat-synthesis machinery, producing a short branched fatty acid. In the final step, a single enzyme links the vanillylamine to the fatty acid chain, and the result is capsaicin. That final enzyme is the one encoded by the Pun1 gene, which explains why losing it eliminates heat entirely.
Capsaicin isn’t alone in the pepper. It belongs to a family of related compounds called capsaicinoids. Dihydrocapsaicin is the second most abundant and contributes roughly as much heat as capsaicin itself. Smaller amounts of nordihydrocapsaicin, homocapsaicin, and homodihydrocapsaicin round out the group. Together, these compounds account for the full heat profile of any given pepper, though capsaicin and dihydrocapsaicin make up about 90% of the total.
Why Peppers Evolved to Be Hot
Capsaicin didn’t evolve to spice up human food. Research on wild chilies in Bolivia revealed that the compound serves as a defense against fungal infection, specifically a seed-killing mold called Fusarium. This fungus invades pepper fruits through tiny holes left by insect bites and destroys the seeds inside. In experiments, capsaicinoids directly inhibited Fusarium growth and protected seeds from being killed before they could be dispersed.
Wild chili populations in wetter, more fungus-prone environments tend to produce more pungent fruits, while populations in drier areas are often mild or completely sweet. This pattern strongly suggests that capsaicin production is an adaptive response to microbial pressure rather than a defense aimed at animals.
There’s an elegant twist in the system. Birds are completely insensitive to capsaicin because their pain receptors don’t respond to it. Mammals, on the other hand, feel the burn intensely. Since birds swallow pepper seeds whole and deposit them intact in their droppings, while mammals tend to crush seeds with their teeth, capsaicin effectively steers the fruit toward the dispersers that help the plant reproduce and away from the ones that destroy its seeds.
How Capsaicin Is Extracted Commercially
For use in pain-relief patches, pepper sprays, and food-grade hot sauces, capsaicin is extracted from dried peppers on an industrial scale. The traditional method uses hexane as a solvent, which is effective but toxic and leaves residue that must be carefully removed. Newer approaches favor ethanol-based extraction, using around 95% alcohol to pull capsaicin out of dried, ground pepper material.
Two common techniques are Soxhlet extraction, which cycles hot solvent through the pepper material repeatedly, and ultrasound-assisted extraction, which uses sound waves to create microscopic pressure changes in the solvent. These pressure changes break open plant cells more efficiently, increasing the amount of capsaicin recovered in less time. Both methods work well at about 30 minutes of processing with a 95% ethanol solution, though ultrasound-assisted extraction tends to yield slightly more capsaicin because the sound waves physically drive the solvent deeper into the plant tissue.
A Brief History of Its Discovery
Humans have been eating chili peppers for at least 6,000 years, but identifying the specific molecule behind the heat took until the 19th century. A chemist named Bucholz first isolated capsaicin in a partially purified crystalline form in 1816. Sixty years later, in 1876, a researcher named Thresh obtained it in pure crystalline form and gave it the name capsaicin, derived from the Capsicum genus. The compound’s full chemical structure wasn’t worked out until the early 20th century, and synthetic capsaicin became available shortly after.