Do all peppers produce capsaicin? The truth about pepper heat

January 6, 2026 •

4 min read

The Scoville scale, developed in 1912 by pharmacist Wilbur Scoville, measures the pungency of chili peppers. However, the notion that all peppers contribute to this scale is incorrect, as some peppers completely lack the chemical responsible for the heat sensation.

Quick Summary

Not all peppers produce capsaicin; bell peppers, for example, contain a recessive gene preventing this production. The compound is concentrated in the internal placenta and ribs, not the seeds, explaining why some peppers are hot and others are mild or sweet.

Key Points

Genetic Variation: Not all peppers produce capsaicin due to genetic differences; bell peppers, for instance, have a recessive gene that prevents it.
Heat Source Location: Capsaicin is most concentrated in the internal placental tissue and ribs of a pepper, not the seeds as commonly believed.
Environmental Impact: Factors like water stress, sunlight, and soil conditions can affect a pepper's final capsaicin concentration, with stressed plants often producing hotter peppers.
Scoville Scale: The Scoville scale is used to measure a pepper's pungency, with peppers like the bell pepper registering a score of zero.
Evolutionary Purpose: Capsaicin serves as a defense mechanism for pepper plants against mammals, while birds, which are unaffected, help disperse the seeds.
Breeding for Mildness: Plant breeders have created heatless varieties of typically hot peppers, like the 'Habanada', allowing for flavor without pungency.

Not All Peppers Are Created Equal: The Capsaicin Gene

Not all peppers produce capsaicin, the chemical compound responsible for the burning sensation associated with spicy foods. This biological fact is a result of genetics, with some pepper varieties lacking the ability to produce this pungent compound. The most prominent example is the common bell pepper, which possesses a recessive gene that effectively turns off capsaicin production. The genetic makeup of a pepper is the primary determinant of its heat level, explaining the vast range of spiciness, from a sweet bell pepper with zero Scoville Heat Units (SHU) to a scorching Carolina Reaper with millions of SHUs.

The Science Behind the Scoville Scale

Developed in 1912, the Scoville scale measures the concentration of capsaicinoids in a pepper, with capsaicin being the most abundant and potent. Early methods relied on human taste testers, but modern techniques use High-Performance Liquid Chromatography (HPLC) for more precise and reliable results. The concentration of capsaicinoids is not uniform throughout the pepper. Contrary to popular belief, the seeds are not the main source of heat. Capsaicin is primarily synthesized and stored in the pepper's placenta, the white spongy tissue that the seeds attach to. The seeds themselves may carry some heat due to their proximity to the placenta but do not produce the compound.

Environmental Factors That Influence Capsaicin Levels

While genetics sets the potential heat level, environmental factors can significantly influence the final capsaicin concentration. A pepper variety that is typically hot can produce milder fruit if its growing conditions are too favorable.

Water Stress: Plants that experience moderate water stress tend to produce hotter peppers. Overwatering can dilute the capsaicin, resulting in a milder flavor.
Sunlight and Temperature: Hotter, drier conditions tend to increase the pungency of peppers. Peppers grown in cooler, shadier locations may have a milder heat profile.
Nutrient Levels: Deficiencies in key nutrients, such as nitrogen, can stress the plant and affect overall health, which in turn can impact capsaicin production.
Harvest Time: Capsaicin concentrations tend to increase as the pepper ripens. A fully mature red chili will generally be hotter than a younger, green one from the same plant.

Comparison of Peppers with and without Capsaicin


Feature	Capsaicin-Producing Peppers (e.g., Jalapeño, Habanero)	Non-Capsaicin-Producing Peppers (e.g., Bell Pepper)
Pungency	Can range from mildly spicy to extremely hot.	Not spicy; considered sweet.
Capsaicin Source	Contains capsaicin concentrated in the placental tissue and ribs.	Contains a recessive gene that prevents the synthesis of capsaicin.
Scoville Rating	Higher on the Scoville scale (e.g., Jalapeños 2,500-8,000 SHU).	Zero on the Scoville scale.
Flavor Profile	Often described as having a fruity, smoky, or earthy undertone in addition to heat.	Sweet and crisp with no heat.
Appearance	Varies widely in size, shape, and color depending on the cultivar.	Recognizable 'bell' shape; comes in green, red, yellow, orange, and purple.

Beyond the Bell: Other Non-Pungent Peppers

While bell peppers are the most well-known example of a capsaicin-free variety, they are not the only ones. Plant breeders have developed special cultivars of typically hot peppers that lack the characteristic heat. An example is the 'Habanada', a heatless variety of habanero. Another is the 'Coolpeno', a heatless jalapeño. These non-pungent peppers allow people to enjoy the unique flavor profile of chili peppers without the intense burn. Interestingly, some typically mild varieties, like sweet banana peppers or paprika, can also have very low or negligible amounts of capsaicin. The 'Mexibelle', a hybrid bell pepper, contains a small amount of capsaicin, demonstrating that genetic traits can be manipulated to produce varying heat levels.

The Purpose of Capsaicin

For the pepper plant, producing capsaicin is a strategic survival mechanism. The compound deters mammals from eating the fruit, as mammals chew the seeds and destroy them. Birds, however, are unaffected by capsaicin and can eat the fruit without harm, spreading the seeds over a wide area. This evolutionary adaptation benefits the plant's propagation. Additionally, research suggests that capsaicin may act as an antifungal agent, protecting the seeds from fungal pathogens. The production of capsaicin is energy-intensive for the plant, which is why environmental factors can influence how much of the compound is produced. For more information on the specific genes involved, explore studies such as this one from the National Institutes of Health.

Conclusion

The simple answer to the question, "Do all peppers produce capsaicin?" is no. The presence of this fiery compound is not universal but rather a function of a pepper's genetics and environment. While hot peppers evolved to use capsaicin as a defense mechanism, selective breeding and natural genetic variations have produced a wide range of peppers, from the sweet and mild to the intensely pungent. The next time you encounter a pepper with no heat, you'll know that a little recessive gene is responsible for your mild culinary experience.

Frequently Asked Questions

The hottest part of a pepper is the placenta, the white spongy tissue inside to which the seeds are attached.

No, bell peppers do not contain any capsaicin due to a recessive gene, giving them a Scoville rating of zero.

Removing the seeds, along with the attached placenta and ribs, will significantly reduce a pepper's heat, as this is where most of the capsaicin is concentrated.

No, cross-pollination does not affect the heat level of the current season's fruit. It can, however, affect the seeds, meaning the resulting peppers from those seeds the following year might be hotter.

Differences in heat can be caused by environmental factors like water stress, sunlight exposure, and soil composition during the plant's growth cycle.

Yes, a common method is to look for white stretch marks or corking on the pepper's skin. The more of these marks, the more stressed the plant likely was, and the hotter the pepper tends to be.

Capsaicin is the most abundant and potent of a larger group of related compounds called capsaicinoids. Capsaicinoids are responsible for a pepper's pungency.