What chilies do
Chillies have been used in cookery for thousands of years, initially by Native and Mesoamericans, then later in the Old World: prior to this mustard (Brassica nigra), horseradish (Radicula armoracia) and pepper (Piper nigrum) were used to give food a kick. These don’t contain capsaicin: the chemicals that give you the kick in these are quite different. In mustard and horseradish, two glycosides called myristin and sinigrin are present: when these are hydrolysed by the action of enzymes, they release allyl isothiocyanate. Onions and garlic (Allium spp.) release the similarly pungent allyl thiosulfinate when bruised. The alkaloid piperine is responsible for the heat of conventional pepper. All these compounds are relatively water soluble and volatile, which is why a glass of water and some deep breathing will fix most of the pain of OD-ing on these.
Chillies are different, because the active principle is very water insoluble. The main effect of chillies is the burning sensation you’ll all be very familiar with. Capsaicin stimulates receptors on the tongue (and elsewhere, as anyone who’s OD-ed on chillies and spent the next day on the toilet with a ring-stinger will know) to release calcium ions, which trigger pain signals to the brain along the trigeminal nerve. People who eat a lot of chillies gradually build up a tolerance to their effects, which is why an ancho will blow the head off someone who’s never eaten chillies before, whereas a seasoned addict will be able to eat jalapeños like they were canapes. A second side effect of the stimulation of pain receptors is the release of endorphins, which are peptides (tiny proteins) in the brain, which stimulate the same pain-killing receptors that heroin and morphine bind to. Hence the rush that many chilli stuffers get, which is similar to the runners’ high that people who work-out a lot get. They make me feel a bit light headed and floaty, which is very pleasant.
The medical uses of capsaicins and chillies are quite varied. They have a warming effect on the skin if added topically, which is useful for aching joints, and related to this is their circulatory stimulatory effect: the flushing and sweating you get if you overdo them. Intestinal parasites don’t like them any more than you ought to, so they have been used in herbal medicine to purge parasitic worms. Because they increase your pain threshold (by increasing the threshold stimulation nerves need before they start firing), they have also been used experimentally in the treatment of neuralgia. They also seem to help treat mouth ulcers. And they contain more vitamin C than citrus fruits.
A not very medical use of capsaicin has been in pepper sprays, which cause extreme pain when sprayed on mucous membranes, as anyone who has tried taking out contact lenses or having a w*nk after preparing chillies without first washing their hands very thoroughly in detergent will testify. Capsaicin is widely used as a mammal repellent: both in bird seed (squirrels don’t like it), and in rubbish bin repellents to stop the local cats pulling fish heads out of your bin bags and all over your lawn. Another interesting application is as a marine antifoulant: the idea being that ships whose hulls are painted with chilli will be too ‘hot’ for barnacles to attach to.
