Capsaicin is a chemical that is produced by chili peppers which is the cause of the heat in every hot chili recipe.

Do You Know What Makes Your Chili Hot?

Ever wonder why some chili is mild and other chili recipes are so
hot that your eyes water and your lips burn?  It all comes down
to one specific chemical called capsaicin.

Capsaicin is produced by chili peppers as an irritant to mammals.
The irritant properties of capsaicin cause heightened levels of
endorphins in the body which could explain why some humans enjoy the
burning sensations that accompany the ingestion of capsaicin.
To further explain, the high levels of endorphins cause a natural
high which some people can’t seem to get enough of.

Capsaicin is found in the parts of chile peppers that are white
and vein like, also known as the placental parts of the chile.  The white covering which
holds the seeds in place in the chili peppers has the highest
concentration of capsaicin, and the lowest concentration can be
found in the fleshy parts of the peppers.

So exactly how hot is capsaicin?  The heat value is usually
measured in a somewhat subjective way by Scoville Heat Units.
The method used in determining the heat value involves diluting
various amounts of dried chili peppers in sugar water and measuring
how hot it is when someone sips the liquid concoction. 

While Scoville Units are still widely used today, more and more scientists
are leaning toward high performance liquid chromatography to
accurately measure the amount of capsaicin in chili peppers.
While this method is more accurate, you must keep in mind that the
levels of capsaicin in certain peppers will vary according to soil,
water, and other growing conditions.

The mild bell pepper ranks the lowest on the Scoville scale with
habanero and scotch bonnet ranking as two of the hottest peppers.
The Scoville units for habaneros and scotch bonnets range from
100,000 to 500,000.  The more commonly known jalapeno falls in
the middle with a range of 2,500 to 8,000 Scoville units.  A
more detailed chart of Scoville Heat Units can be found here.

So if you’re looking to heat up your chili recipe today, then add
a finely chopped habenero to the chili during the cooking process.
If you want a mild chili with just a bit of pepper flavor, then use
red, green and yellow bell peppers.  These also add some great
color to any chili recipe.

On a final note, there are a few safety issues that you should be
aware of when handling the hotter chili peppers.  Capsaicin
will burn your eyes (after all it is an irritant and is the main
ingredient in police pepper spray).  Capsaicin is not water
soluble which means that it will not rinse off with water.
With that said, wear gloves while handling the peppers and keep your hands away from your eyes!