The warmer regions of the American continent were originally the natural habitat of all species of chili peppers (the genus Capsicum). This fact seems a bit strange at first because chili peppers are now widespread in all corners of the world. They are grown worldwide and spice countless dishes. You could be temped to think that the chilies would have grown on all continents in a distant past, but you would be wrong.
It is generally accepted that there are about 30 different species of chili peppers. The most commonly used, however, is the rather sharp Capsicum annuum. This is the one you commonly see in our supermarkets. It is the tamed version of a wild ancestor that must have grown somewhere in the inhospitable border region of Brazil and Colombia. Viewed botanically, the colourful edible chili pepper is no fruit, but a berry.
The first part of its scientific name, Capsicum, is of Latin origin. The word Capsa is translated as 'box' or 'holder' and is related to the Latin verb Capere, which means 'to grab' or 'to hold'. The second part, annuum, is easy to explain, because the Latin annus means 'year'. It is therefore considered an annual plant, but the strange thing is that the chili pepper isn't strictly an annual in every sense: if no frost occurs during the wintertime, the plant is able to survive and can grow into a large perennial shrub.
In the olden days, when doctors had to resort to the kingdom of the plants to ward off disease, the exotic chili was prescribed extensively. It was thought it was the most effective cure to fight acute diphtheria and scarlet fever. The latter disease is caused by a bacterial infection. It was a major cause of death in the Middle Ages, but nowadays it can be successfully treated with antibiotics. It is of course highly questionable if chili peppers truly had a positive effect on these maladies.
The chili peppers contain an unusually high amount of vitamin C, even more than a lemon of similar weight. Thus, they are rather healthy, though you will usually use just a small amount of chili peppers in your dishes. Next to all sorts of other healthy ingredients, chili peppers also contain varying amounts of a substance called capsaicin. It is an alkaloid which stimulates the receptors on your tongue. These receptors are sensitive to pain and heat. This then gives you that sharp burning sensation in your mouth. If you love your spicy foods, your body will slowly but surely get used to the capsaicin and you'll have less problems with the spiciness.
But not every chili pepper is the same. Every variety contains different levels of capsaicin. In order to measure the pungency of a certain variety, the Scoville Scale has been adopted. On this scale, mild family members like the tomato or the paprika are set at zero, the Cayenne pepper might sometimes reach levels of 50,000, while the world record holder, the Carolina Reaper, surpasses an eye-watering two million on that scale. That's really hot!
There are a couple of simple rules of thumb to determine the pungency of most chili peppers: the smaller the chili, the sharper it will be and the sharpness will reduce when when the pepper discolours from green (immature) to red (ripe).
More info: https://www.naturalspices.com/ground-chillies.html