Citronellol is a naturally derived ingredient that is added to cosmetics and personal care products as a fragrance due to its sweet, floral scent.
Citronellol, also known as dihydrogeraniol, is a natural acyclic monoterpenoid (a type of modified terpene). Terpenes are a large and diverse class of organic compounds produced by a variety of plants. They often have a strong scent and may protect the plants that produce them by deterring herbivores and by attracting predators and parasites of herbivores.
Citronellol exists as two enantiomers in nature. An enantiomer, also called an isomer, refers to a chiral molecule that is non-superimposable on its mirror image. (+)-Citronellol, which is found in citronella oils, including Cymbopogon nardus (50%), is the more common isomer. (−)-Citronellol is found in the oils of rose (18 to 55%) and Pelargonium geraniums. According to Toxicology Data Network, citronellol has been reported in about 70 essential oils, for instance, citronella, rose, geranium, neroli, chamomile, tagetes, lemongrass, basil and lavender.
There are two primary types of citronella that contain citronellol as an active constituent: the Java type and the Ceylon type. Both originally come from parts of Asia, especially grassy areas of Sri Lanka. The Java type contains 10.45 percent citronellol and has a scent similar to lemon and lemongrass. The Ceylon type contains 11.85 citronellol and has a scent similar to citrus fruits, wood, and cinnamon.
Citronellol functions as a fragrance ingredient and insect repellent when used in personal care products.
In perfumes, citronellol functions as a fragrance enhancer since it has the ability to enhance the aromas of floral types, especially rose. In the skin care industry, citronellol is prominently used as a fragrance ingredient for cosmetics and personal care products. According to L’Oreal Paris, research studies show topical application of citronellol has low permeability and potency, which demonstrates good skin tolerability. For this reason, citronellol is a desirable skin care ingredient to infuse into products, such as shampoos, lotions, creams, shaving creams, and bath products, to provide a sweet, floral scent.
You may be familiar with citronellol since it is one of the active components of citronella oil insect repellents and citronella candles. In fact, citronella has been registered as a gentle, plant-based insect repellent in the U.S. since 1948. Citronellol effectively functions as a mosquito repellent at short distances, but protection greatly lessens when the subject is slightly further from the source. Citronella insect repellents have even been shown to repel dangerous Aedes aegypti mosquitoes, which are capable of spreading dengue fever and the Zika virus.
The United States Food and Drug Administration (FDA) considers citronellol as generally recognized as safe (GRAS) for direct addition to food. The Cosmetic Ingredient Review (CIR) Expert Panel defers review of individual fragrance ingredients to the International Fragrance Association (IFRA) program unless the ingredient has significant uses other than as a fragrance.
The safety of citronellol has been evaluated by the Research Institute for Fragrance Materials Expert Panel (REXPAN). Based on this evaluation, an IFRA Standard has been established which restricts the use of citronellol in fragrances because of potential sensitization. However, the degree to which citronellol can cause an allergic reaction in humans is disputed.
As mentioned above, citronellol has low permeability when applied to the skin, which means it is not absorbed into the deeper layers of skin. However, skin care expert Paula Begoun explains that when products containing citronellol are applied to the skin, a problem arises when citronellol is exposed to air. This exposure causes the unstable citronellol molecule to oxidize, which is believed to trigger aggravation on skin.
According to EWG, citronellol is rated as a 5 on a scale of 1 to 10, with 1 being the lowest risk to health and 10 being the highest. The main concern cited by EWG regarding citronellol is “possible human immune system toxicant or allergen”.
Due to the possibility of an allergic reaction, those with sensitive skin should try to avoid citronellol or perform a patch test with any product containing this ingredient.
References for this information: Wikipedia, “Citronellol”, Wikipedia, “Terpenes”, Toxicology Data Network, “Citronellol”, Cosmetics Info, “Citronellol”, Dr. Josh Axe, “Citronella Oil: Repel Insects, Pain & Stress!”, Paula’s Choice, “Citronellol”, EWG’s Skin Deep Cosmetic Database, “Citronellol”, L’Oreal Paris, “Citronellol”.