What Makes Peppers Spicy?

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You know how it feels to eat spicy food. Humans have been using hot peppers in cooking for millennia. But have you ever wondered what makes peppers spicy? In this article, I’ll share the science behind what makes spicy chilies “hot,” and some helpful tips to reduce the pain (if you’re in need).

The main cause of the heat in peppers is the chemical compound capsaicin, which binds with pain receptors in our tissue, causing a burning sensation. It is found abundantly in many Capsicum varieties.

What Is Capsaicin?

You may not have heard of capsaicin, but you have probably felt its effect. Capsaicin is a chemical compound that is naturally found in some peppers. When contact is made with human tissue, capsaicin causes a burning sensation. Without it, peppers wouldn’t be spicy.

This is what capsaicin looks like to a scientist:

Capsaicin molecular structure

Why do peppers contain capsaicin?

Scientists originally thought capsaicin was in peppers to deter animals from eating them. However, more recent research indicates that capsaicin is likely produced to prevent insect damage and fungal growth within the peppers. This is likely why stressing pepper plants results in spicier peppers.

Capsaicin binds with certain pain receptors, causing the familiar sensation of heat. However, it is not an actual burn. No damage is caused to the tissue, and instead it just feels painful.

This reaction to capsaicin originally led scientists to believe that the pepper plant used it to deter animals from eating their fruits. This was odd, because most plants actually encourage animals to eat their fruits in order to spread seeds via mobile mammals.

However, stomach acid can cause damage to pepper seeds, but not in birds. Interestingly, birds can’t feel the burn from hot peppers.

“Birds are indifferent to the pain-producing effects of capsaicin and therefore serve as vectors for seed dispersal.”

Birds vs Spicy Peppers

So it all made sense; most animals destroy pepper seeds when they eat them, and they don’t like the pain of eating the peppers. Meanwhile, birds don’t destroy seeds, and they can’t feel the pain of capsaicin. It seemed like the perfect symbiotic relationship between pepper plants and birds for spreading seeds and eating respectively.

However, more recently, capsaicin was found to be helpful in preventing mold growth on peppers in humid climates. This is now accepted as the primary reason that peppers produce capsaicin. The relationship with birds is still likely beneficial to both parties.

Check out this video explaining more interesting research on this topic.

What Is The Hottest Part Of A Pepper?

The highest concentration of capsaicin in peppers is within the placenta or “pith” portion of the flesh. This is the membrane that holds the seeds inside of the pepper. As a result, removing the seeds is often recommended when cooking to reduce the spiciness of a dish. The placenta is also the portion of the pepper to avoid touching while cutting peppers.

Anatomy of a pepper diagram and insides
Pepper Anatomy Diagram.

Capsaicin will cause irritation to any part of your body that it touches, so be careful of the hands, eyes, and any other sensitive skin. If you find yourself with a hot pepper burn on your hands, try some of our remedies here.

Do pepper seeds contain capsaicin?

Pepper seeds are often said to be the spiciest part of a hot pepper. However this is technically not true. The most spicy portion of a pepper is the placenta, or pith, not the seeds themselves.

Pepper seeds often have residual capsaicin on their surface due to contact with the placenta, but the actual seeds do not contain any capsaicin.

pepper seeds

It is still best practice to remove the seeds in order to reduce spiciness when cooking. If you remove the seeds, chances are you will also remove most of the placenta, as the seeds are connected.

Do Peppers Actually Burn You?

After eating a particularly spicy meal, you may begin to panic and wonder if you are in real danger. Can peppers actually burn your mouth and cause damage?

In short, spicy peppers do not cause any actual tissue damage like a real burn would. The capsaicin molecule binds with pain receptors, imitating the sensation of a burn. However, highly-sensitive individuals may want to avoid spicy food. It can cause an upset stomach, vomiting, and long-lasting discomfort.

How To Stop Spicy Pepper Mouth

Did you eat a pepper that was way too hot? It’s pretty easy to find habanero peppers or even ghost peppers at the supermarket. But most are not ready for the intense pain that comes with eating these super spicy peppers.

Here are the 3 best methods for reducing spicy burning in the mouth and lips:

  1. Drink dairy milk. If you have any milk, go drink it. No milk? Try any dairy, like ice cream or yogurt. The compound “casein” in dairy products binds with capsaicin (the spicy molecule) and helps reduce the burn.
  2. Coat your mouth with olive oil. This may seem odd, but capsaicin is an oil based compound that repels water. This means that water will only spread the burn around your mouth. Instead, try swishing a small amount of oil in your mouth and spitting it out.
  3. Eat bread. This doesn’t work as well as drinking milk, but it can help relieve some burn in the mouth, and can also help reduce stomach discomfort (especially when consumed before eating spicy food).

Tip: Avoid getting pepper juices on your lips. This can be more painful and more difficult to cure than heat on the tongue.

How To Stop Spicy Pepper Burn On Skin

Pepper Burn on Hand

Did you cut some hot peppers without gloves? Feeling the burn hours later? This is a painful issue, but thankfully we’ve got 3 great methods for reducing pepper burn on the skin:

  1. Scrub with dish soap. Dish soap is a detergent and can help break remove some of the capsaicin from your skin. Scrub the affected area with dish soap and cold water until you feel relief.
  2. Submerge in milk. Using milk on the skin works the same way that it does in the mouth. Don’t have milk? Try a high proof alcohol or rubbing alcohol instead. Capsaicin is soluble in alcohol.
  3. Don’t shower. Don’t take a shower until you start to feel better. Being exposed to hot water and mist will open your skin pores and exacerbate the burning feeling. You may also spread it around with your hands as you wash yourself. Capsaicin repels water, so the water will not help remove it.

Good to know: Capsaicin does not cause any damage to your tissue. However, without taking action, burning on the skin can last for several hours and even days because there is not any natural flushing as there is in the mouth.

Try one of our methods and you are sure to get some relief from pepper burns on the skin. Got some in the eyes? Get relief here.

Is Capsaicin a Pain Reliever?

While the initial sensation from contacting capsaicin is burning, the chemical compound is actually an analgesic. This means that capsaicin acts to relieve pain on a biological level. This is why many capsaicin creams and gels are sold for those suffering from various conditions.

On a technical level, capsaicin is both a TRPV1 agonist, and a non-narcotic analgesic. Put more simply, capsaicin acts as a pain reliever (analgesic) at the chemical level. It is used to control peripheral nerve pain and is commonly used for people suffering from neuralgia. Ask your doctor before trying this method for pain relief.

The Scoville Scale

The Scoville Scale

Different Pepper Heats

The Scoville Scale ranks peppers in terms of heat level. The scale is measured in “Scoville heat units” or SHUs for short.

Peppers range from 0 to 2,000,000 SHUs and higher. Higher SHU ranking means a higher concentration of the chemical compound capsaicin.

  • Bell peppers contain no capsaicin. These peppers are not spicy whatsoever, but are sweet instead.
  • Jalapeño peppers rank around 5,000 SHUs, and are one of the most common hot peppers.
  • Habanero peppers rank around 200,000 SHUs or more, and are where “spicy” starts to become “painful.”
  • Ghost peppers rank around 1,000,000 SHUs, and were once known as the world’s hottest pepper. That was, until…
  • Carolina Reaper peppers rank around 2.2 million SHUs, and are one of the hottest peppers in the world. Most people wouldn’t touch these with a ten foot pole, nevermind their tongue.

There are many other types of peppers all around the world, ranking all across the Scoville scale. If jalapeños are just not quite enough, but habaneros are too much, use the Scoville scale chart above to find one in the right zone for you.

Want to try one of the world’s hottest peppers? You can grow them yourself!

I hope you learned a lot about what makes peppers spicy throughout this article. Still have questions? Leave us a comment with any thoughts you have below.

Calvin Thumbnail


One of the original Pepper Geeks! When Calvin isn’t gardening or learning more about peppers and botany, he might be traveling new places or playing some music.

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  1. I pureed jalapeño peppers, put them in a plastic bowl, covered with tin foil, and set in fridge. Over the next five days, I removed enough to make one batch of pepper jelly per day. It seems each batch was less spicy. What did I do wrong?

    1. It could be that the soft pith floated on the surface of the bowl and was used first, leaving the flesh for the later batches. Pith is where all the spice is. Otherwise not sure what may have happened.

  2. What stays on the dried Chile powder that makes it hot or mild. If no placenta is left.

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