Last Updated on April 17, 2023 by Verna Meachum

Everyone’s talking about limonene in hair products these days and for good reason! This naturally-occurring compound is full of beneficial properties that help to nourish and strengthen your hair.

From providing instant hydration to fighting scalp conditions, limonene can work wonders on your mane.

But don’t just take our word for it – there are dozens of scientific studies out there to back up the benefits.

Keep reading to find out why this citrus derivative should be part of your regular hair care routine and how to use it safely for maximum results.

What is Limonene? 

Limonene is a naturally occurring organic compound commonly used in food flavoring, soap and cleansing products, skincare, and hair care formulations.

The word “limo” highlights its close relationship with citrus fruits as it is abundantly present in the essential oil extracted from lemon, grapefruit, and mandarin peels.

Limonene is a faint pale yellow liquid having a characteristic lemon-like aroma which is widely used in food and personal care formulation as well as in perfumery products.¹

In recent times, limonene has drawn much attention for its new dimensions of applications as an anti-inflammatory agent, and skin and scalp repair active agent.²

In this article, we investigate the chemical characteristics of this molecule and its application in hair care products.

Additionally, we consider how it can be used topically to benefit scalp and skin health while also exploring its safety profile as well as any potential toxicities that may arise from usage.

D-Limonene vs. L-Limonene

There are two isomers of limonene; D-Lemonine, and L-limonene.

Isomers are two molecules of the same compounds but having different spatial (3D or in space) arrangements of chemical bonds.

Two limonene isomers present distinct aromas and chemical properties – D-Limonene offers an orange aroma, while L-limonene exudes the classic scent of pine.

D-limonene is the focal molecule for the food and cosmetic industry. It is a by-product of the lemon/orange juice industry where fruit peels are used to extract D-limonene.

D-Limonene in Human Consumption: Key Benefits

By virtue of its exceptional solvent capability, D-limonene has been preferred as an alternative to halogenated hydrocarbons in many common household and personal care products.

Limonene is a powerful disinfectant and anti-microbial agent commonly found in household products. In the food industry, it’s also used to provide confectionary items with an invigorating lemon aroma or flavor.

With only a small dosage required, D-limonene is safe for human consumption. In skin care products, it can be used as a component of fragrance or as an active skin conditioning agent.

Studies have shown that D-limonene is capable of healing the skin, combating inflammation on a cellular level, and aiding in wound recovery.

Also, D-limonene acts as a good solvent for lipophilic actives facilitating their absorption and penetration across the lipid bi-layer of the skin stratum corneum. 

In hair care formulation, d-limonene is used as a fragrance component offering a distinct lemon aroma.

For this particular job, it is generally added in small quantities making only a small fraction of the total formulation.

Hair shampoo may also contain D-limonene to impart a citrus cleansing sensation. To improve scalp health, several hair care products feature D-limonene as a key ingredient.

To summarize, here are the principal advantages of using D-limonene in personal care formulations:

● Fragrance component (part of fragrance blend) to give a citrus aroma.

● Wound healing.

● Penetration boosting agent.

● A solvent in skin or scalp care formulations.

● Anti-inflammatory benefits to scalp cells.

Are There Any Benefits to Curly Hair?

It is essential to take into account the concentration level of D-limonene when considering its potential beneficial effects.

For curly hair consumers, D-limonene is a suitable active ingredient to improve scalp health, combat dryness and boost the health of the upper scalp layer.

Curly hair is known for its naturally dry texture that lacks moisture compared to straight virgin, non-chemically treated hair fibers.

Safety and Toxicology for Topical Application

Before we dive into the safety and toxicology for topical application, please note that we only provide comprehensive information relating specifically to the application of D-limonene on the scalp or hair in haircare products.

D-Limonene has been subject to several dermatological and toxicity studies. Recently, this ingredient has been the subject of heated debate. Unfortunately, much of the talk and criticism circulating is based on false information.

The safety and toxicity of any chemical ingredients are contingent upon the amount of ingredient used (concentration of exposure) and time of exposure.

In the USA, D-limonene is characterized as generally recognized as safe (GRAS) for use in food formulation and fragrance additives in cosmetics.

Since D-Limonene used as a fragrance component only contains minimal amounts, it does not pose any threat or adverse effect on the scalp.

Moreover, rinse-off hair care products only stay on the scalp for a very small amount of time. This restricted exposure time ensures that D-Limonene in these types of products listed as a fragrance component does not result in any negative effects.³ 

In addition, scientists have studied the effects of high dosages of D-Limonene when applied directly to the skin and found that it does not cause any discomfort or irritation.

However, D-limonene can cause redness, itchiness, or irritation on sensitive skin. Consumers with sensitive skin should avoid using products containing D-limonene in high dosages. 

Potential Sensitizer

The oxidation of D-limonene may lead to the formation of limonene hydroperoxides, which have been intensively investigated and are potential skin sensitizers.

This oxidation takes place when products are exposed to exposure to heat and solar radiation.

Products containing D-limonene should be kept in the dark in a cold dry place and away from direct solar radiation.^4–5

Notably, D-limonene itself has no adverse effects when applied topically; however, its oxidized derivatives can sensitize the skin.

The potential adverse effects that can happen to the skin due to oxidized limonene are:

● Allergic response

● Redness

● Itchiness

● Irritation

Safety for Kids

As previously noted, D-limonene’s safety is contingent upon its intended purpose.

With hair care items, a low dose of D-limonene is entirely safe for children. It is essential to note that D-limonene should not be used in its unadulterated form directly on the skin.

Also, products containing D-limonene should be appropriately stored away from heat and sunlight to maintain their effectiveness.

Summary

Limonene is an organic molecule with an unmistakable citrusy smell commonly used in food and cosmetics. This distinct scent adds complexity to beauty products, resulting in a delightful fragrance that you won’t forget.

In accordance with current regulations, it is harmless to incorporate D-limonene in hair care products.

Great caution must be taken to avoid the oxidation of limonene and to keep it protected from direct sunlight and sources of heat.

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References

1. Fahlbusch, K.-G.; Hammerschmidt, F.-J., Ullmann’s Encyclopedia of Industrial Chemistry. In Flavors and Fragrances, John Wiley & Sons: 2003.

2. A d’Alessio, P.; Mirshahi, M.; Bisson, J.-F.; C Bene, M., Skin repair properties of d-Limonene and perillyl alcohol in murine models. Anti-Inflammatory & Anti-Allergy Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry-Anti-Inflammatory and Anti-Allergy Agents) 2014, 13 (1), 29-35.

3. Ravichandran, C.; Badgujar, P. C.; Gundev, P.; Upadhyay, A., Review of toxicological assessment of d-limonene, a food and cosmetics additive. Food and Chemical Toxicology 2018, 120, 668-680.

4. Matura, M.; Goossens, A.; Bordalo, O.; Garcia-Bravo, B.; Magnussona, K.; Wrangsjö, K.; Karlberg, A.-T., Oxidized citrus oil (R-limonene): a frequent skin sensitizer in Europe. J. Am. Acad. Dermatol. 2002, 47 (5), 709-714.

5. Bråred Christensson, J.; Andersen, K. E.; Bruze, M.; Johansen, J. D.; Garcia‐Bravo, B.; Gimenez Arnau, A.; Goh, C. L.; Nixon, R.; White, I. R., Positive patch test reactions to oxidized limonene: exposure and relevance. Contact Dermatitis 2014, 71 (5), 264-272.