Chilli is central to cuisines across Asia, Africa and the Americas, and it arrived in most of them within the past five hundred years, which is a surprisingly recent transformation.
What capsaicin does
It binds to a receptor that responds to heat and to physical abrasion.
Which means the brain interprets the signal as burning, despite no temperature change and no tissue damage.
The sensation is genuinely pain rather than taste, transmitted by a different system from the taste receptors.
Which is why it can be felt anywhere with the relevant receptors rather than only on the tongue.
Why people seek it
The pain response triggers release of endorphins, which produces a mild pleasurable effect afterwards.
Which is one proposed explanation for why the sensation becomes sought rather than avoided.
Another is benign masochism — enjoyment of a sensation known to be harmless despite the alarm signal, similar to enjoyment of frightening films.
Both have some support and neither is established.
Tolerance
Repeated exposure desensitises the receptors, which is why regular consumers tolerate far more.
The effect is genuine physiological adaptation rather than habituation to the experience.
It also reverses with abstinence, which is why tolerance falls after a period without.
The spread
Chillies originated in the Americas and travelled through the trading routes established in the sixteenth century.
They were adopted rapidly in tropical and subtropical regions, where they grew readily and where existing cuisines already used pungent spices.
Which meant they substituted for and supplemented ingredients like black pepper, at a fraction of the cost since they could be grown locally.
That economic factor is probably the largest single reason for the speed of adoption.
The preservation argument
A frequently repeated claim is that spices were used in hot climates for antimicrobial effect.
Several spices do have antimicrobial properties in laboratory conditions.
Whether that explains culinary use has been argued both ways, with correlational studies supporting it and critics pointing out that correlation with climate has other explanations, including that the spices grow there.
The honest position is that it is plausible and not established.
Measuring heat
The traditional scale measured how much dilution was needed before a panel could no longer detect the heat.
Modern measurement uses chemical analysis of capsaicinoid content and converts to the same scale.
Which means published figures are more precise than the original method allowed, and the scale is logarithmic in effect rather than linear in perception.
Relieving it
Capsaicin is fat-soluble and not water-soluble.
Which is why water spreads it around rather than removing it, and why dairy works — the fat dissolves it and the casein proteins help lift it away.
Sugar, starch and oil all provide some relief. Alcohol dissolves it and is not concentrated enough in most drinks to help much.
Cooking with it
Heat is concentrated in the placental tissue holding the seeds rather than in the seeds themselves, which is why removing that reduces heat substantially.
Drying, smoking and fermenting all change the character considerably, which is why the same chilli in different forms produces different results.
And whole chillies added to a dish contribute aroma with limited heat, while chopped or ground ones release it fully, which is a technique decision.
Varieties and their characters
Heat is one dimension and flavour is another entirely.
Some chillies are fruity, some smoky, some earthy, some grassy, and the heat level does not predict which.
Which means substituting one for another changes the dish substantially beyond the heat.
Dried chillies differ from fresh ones of the same variety, since drying concentrates and transforms the compounds.
Preparation methods
Toasting dried chillies before use develops flavour, and burning them produces bitterness that cannot be removed.
Soaking and blending produces a paste that distributes evenly.
Fermenting produces sauces with an entirely different character.
Smoking produces yet another, which is why the smoked version of a chilli has its own name in several languages.
Handling
Capsaicin transfers to hands and from hands to eyes and other sensitive areas, where it is genuinely painful.
Which is why gloves are advisable for large quantities of hot varieties, and why washing with soap and oil works better than water alone.
Health claims
Capsaicin has been studied for metabolic and pain applications, with topical formulations used clinically for certain pain conditions.
Dietary claims about metabolism and weight are considerably weaker, with small effects in short studies.
Gastric effects are the other frequent claim — the belief that chilli causes ulcers has not been supported, since the actual cause is generally bacterial.
For people with existing digestive conditions, individual tolerance varies and is worth respecting.
Building tolerance
Gradual regular exposure raises tolerance measurably over weeks.
Which is why people who move to a cuisine using more chilli adapt rather than remaining permanently uncomfortable.
There is no benefit to forcing it, and the adaptation happens with ordinary eating.