Is Coumarin Found in Lemon Peels? The Science Behind Citrus Zest

November 18, 2025 •

4 min read

While the compound coumarin is often associated with other plants like tonka beans and cassia cinnamon, recent studies confirm that several related coumarins and furanocoumarins are indeed found in lemon peels. These compounds, concentrated in the outer, colored part of the peel known as the flavedo, play a role in the plant's defense mechanisms. Understanding their presence helps clarify their potential impact on health and food preparation.

Quick Summary

Lemon peels contain various coumarins and furanocoumarins, though not the same type found in high concentrations in cinnamon. These compounds are concentrated in the outer peel layer (flavedo) rather than the white pith (albedo). They exhibit several biological activities but can also have phototoxic effects in some citrus varieties, though lemons contain lower levels of the most notorious phototoxins. The quantity and type of coumarins vary depending on the specific lemon variety and growing conditions.

Key Points

Yes, lemon peels contain coumarin compounds: Specifically, they contain a variety of coumarins and furanocoumarins, which are different from the classic coumarin found in cassia cinnamon.
Compounds are in the outer peel (flavedo): The highest concentration of coumarins is in the brightly colored, outermost layer of the lemon peel, known as the flavedo.
The white pith (albedo) has almost no coumarins: The bitter white layer underneath the zest contains virtually none of these compounds.
Lemons have lower phototoxicity risk than limes: While lemons contain phototoxic furanocoumarins like bergapten, the concentrations are lower than those found in limes and bergamot, posing a lesser risk of phytophotodermatitis.
Health effects depend on intake: Low dietary intake from zest is generally safe, while high concentrations in essential oils or extracts could have stronger biological effects, both beneficial and potentially harmful.
Coumarins serve a protective purpose in the plant: These chemicals are concentrated in the outer layer to help defend the plant against pests and pathogens.

The Composition of Lemon Peel

Lemon peel, or zest, is a complex mixture of natural compounds that contribute to its flavor, aroma, and medicinal properties. The outermost layer, the flavedo, is rich in essential oils and various phytochemicals, including flavonoids and coumarins. Unlike the more common coumarin found in high concentrations in cassia cinnamon, the types found in lemons are structurally different and include furanocoumarins.

Key Coumarins in Lemon Peel

Research has identified several specific coumarins and furanocoumarins in the flavedo of Citrus limon. Prominent examples include:

Citropten: One of the most abundant coumarins found in lemon peel extracts.
Bergamottin: A furanocoumarin that is also a key component.
5-Geranyloxy-7-methoxycoumarin (5G7MC): Another major coumarin variant present.
8-geranyloxypsoralen: A furanocoumarin isolated during studies on the chemopreventive properties of lemon peel.

Where Coumarins are Located in the Peel

Studies confirm that these coumarins are not uniformly distributed throughout the lemon's skin. They are concentrated almost exclusively in the flavedo, the thin, colorful outer layer. The inner, white pithy layer, known as the albedo, contains virtually none of these compounds. This is an important distinction for those who zest their lemons, as the goal is to only grate the colored part of the skin and avoid the bitter albedo. The high concentration in the outer layer suggests a role in the plant's defense against pathogens.

Potential Health Effects and Risks

The compounds in lemon peel have both beneficial properties and potential risks, depending on concentration and individual sensitivity. While often praised for their antioxidant and anti-inflammatory effects in studies, the furanocoumarins in citrus can also be phototoxic.

Beneficial Properties

Antioxidant: Coumarins exhibit significant antioxidant activity, helping to protect cells from damage caused by free radicals.
Anti-inflammatory: Some studies suggest that coumarins and their derivatives have anti-inflammatory effects.
Anti-adipogenic: Certain lemon peel coumarins have shown potential in animal studies to inhibit the formation of fat cells, an area of growing research interest.
Antimicrobial: Extracts from lemon peel have demonstrated antibacterial properties against various pathogens.

Potential Risks and Differences with Other Citrus

Phototoxicity: Furanocoumarins like bergapten can cause phytophotodermatitis, a skin reaction when exposed to UV light. While most famously associated with high concentrations in limes and bergamot oil, lemons contain lower levels of the most potent phototoxins.
Hepatotoxicity: Animal studies have shown that high doses of coumarin can cause liver damage. However, the levels found in food are generally considered safe, and it's essential to differentiate between high-dose extracts used in research and the typical dietary consumption from zest.

Coumarin Content: Lemon vs. Lime

The coumarin and furanocoumarin profiles vary significantly across different citrus species, which impacts their phototoxicity and other biological effects. Lemons generally pose a lower phototoxic risk than limes due to their distinct phytochemical makeup.


Feature	Lemon Peel	Lime Peel (e.g., Persian & Key)
Primary Coumarins	Citropten, 5-geranyloxy-7-methoxycoumarin (5G7MC), bergamottin, 8-geranyloxypsoralen	Limettin, bergapten, isopimpinellin, xanthotoxin, psoralen
Concentration Location	Concentrated almost exclusively in the outer flavedo layer	Concentrated in the rind, with varying levels between Persian and Key limes
Phototoxicity Potential	Relatively low compared to limes due to lower concentrations of potent phototoxins	Higher potential for causing phytophotodermatitis due to higher levels of phototoxic compounds like bergapten and xanthotoxin
Dominant Compounds	Often citropten and bergamottin, depending on the variety	Limettin and bergapten, often in higher concentrations than found in lemon
Risk of Reaction	Low risk from normal food consumption; issues arise primarily from concentrated oils or excessive, prolonged topical use	Higher risk, especially with essential oils or prolonged skin contact followed by sun exposure

Preparing and Using Lemon Peel Safely

For most home cooks, the amount of coumarin consumed from lemon zest is minimal and poses no health risk. The primary goal is to use the aromatic flavedo while avoiding the bitter albedo. This is achieved with proper zesting techniques. When using essential oils extracted from lemon peel, which contain concentrated coumarins, it's prudent to be more cautious, especially for cosmetic use where sun exposure could be a factor. Some industrial processing methods use supercritical fluid extraction to specifically remove furanocoumarins from essential oils for fragrance and cosmetic applications.

Conclusion

In conclusion, yes, coumarin compounds are found in lemon peels, though it is crucial to recognize that the types and concentrations differ significantly from other sources like cassia cinnamon. Specifically, the outer, colored part of the peel, the flavedo, contains various coumarins and furanocoumarins, including bergamottin and citropten. These compounds are primarily a byproduct of the plant's defense mechanisms and have demonstrated interesting biological activities in research. However, the concentration is low enough that for most culinary applications, the amount consumed poses no significant risk to human health. While a potential for phototoxic reactions exists due to furanocoumarins, particularly with concentrated oils, the risk from normal dietary intake is negligible compared to other citrus like limes. The vast majority of people can continue to enjoy the flavor and nutritional benefits of lemon zest without concern. For anyone with sensitivities, moderation and awareness remain key. One excellent resource for further reading on the complex chemistry of citrus is the article "Coumarins in the Flavedo of Citrus limon Varieties—Ethanol and Natural Deep Eutectic Solvent Extraction" on the Wiley Online Library.

Frequently Asked Questions

No, the coumarins found in lemon peels, primarily furanocoumarins like bergamottin, are different from the type of coumarin found in cassia cinnamon. While both belong to the same family of compounds, they have different chemical structures and effects.

At the levels typically consumed from zesting lemons for culinary purposes, the coumarins are not considered toxic. High doses, like those used in some animal studies, have shown potential for liver toxicity, but this is far beyond normal dietary intake.

It is possible, though rare, to get a skin rash, or phytophotodermatitis, from handling citrus peels containing furanocoumarins and then being exposed to UV light. Lemons have a lower risk than limes or bergamot, and the reaction typically requires prolonged skin contact with the peel's oil in combination with sun exposure.

The coumarins are located almost exclusively in the flavedo, which is the outer, colored layer of the lemon peel, and not in the white, inner pith (albedo).

Yes, many citrus fruits contain coumarins and furanocoumarins in their peels, though the specific compounds and concentrations vary by species. For example, limes tend to have a higher concentration of certain phototoxic furanocoumarins than lemons.

Cold-pressed lemon essential oils and extracts, which are derived from the peel, contain concentrated coumarins and furanocoumarins. The concentration is much higher than in the peel itself, which is why commercial products are sometimes processed to remove them.

Yes, it is generally very safe to use lemon zest for cooking. The amounts of coumarin and related compounds ingested from typical culinary use are minute and pose no health concerns for the vast majority of people.