Citral is a naturally derived ingredient that is added to cosmetics and personal care products as a fragrance due to its pleasant citrus scent.
Citral, also referred to as lemonal, is either a pair or a mixture of terpenoids. The terpenoids are a large and diverse class of naturally occurring organic chemicals derived from terpenes. While the term “terpenoid” is often used interchangeably with “terpene”, they are actually different. Terpenes are hydrocarbons, which means they consist entirely of carbon and hydrogen, while terpenoids contain additional functional groups.
Citral exists as two double bond isomers. The E-isomer is known as geranial, or citral A. The Z-isomer is known as neral, or citral B. Citral is present in the oils of several plants, including the following:
- Lemon myrtle (90 to 98%)
- Lemongrass (65 to 85%)
- Lemon verbena (30 to 35%)
- Lime (6 to 9%)
- Lemon (2 to 5%)
Citral can be colorless or a pale, yellow liquid. It is used to formulate a variety of cosmetics and personal care products, including aftershave lotions, bath products, moisturizers, perfumes and colognes, and many more skin and hair care products.
Citral is an aroma compound used in cosmetics, perfumes, and personal care products for its citrus scent. The E-isomer of citral, geranial, has a strong lemon (citrus) scent, while the Z-isomer, neral, has a less intense but sweeter lemon scent.
In addition to functioning as a fragrance ingredient, citral has been shown to provide strong antimicrobial properties. A study published in Letters in Applied Microbiology found that citral showed appreciable antimicrobial activity against both gram positive and gram negative bacteria, as well as fungi. Additionally, the study found that the antimicrobial activity of citral was optimized at an alkaline pH. Thus, citral may be used as a preservative in the formulation of cosmetics and personal care products.
Citral also possesses anti-inflammatory properties. A 2017 study on mice found that citral showed a significant decrease in TNF-α (Tumor Necrosis Factor alpha) levels in tests demonstrating anti-inflammatory activity. TNF-α is as a key regulator of the inflammatory response. Vascular endothelial cells respond to TNF-α by undergoing a number of pro-inflammatory changes. Thus, by decreasing TNF-α levels, citral functions as an anti-inflammatory agent.
Citral is one of the active components of citronella oil, which is a common ingredient used in insect repellents and citronella candles. In fact, citronella has been registered as a gentle, plant-based insect repellent in the United States since 1948. Some evidence suggests that citral, as well as the other active compounds in citronella, interfere with mosquito olfactory receptors. 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) includes citral on its list of substances considered Generally Recognized As Safe (GRAS) as a synthetic flavoring substance. The safety of citral has been evaluated by the Research Institute for Fragrance Materials Expert Panel (REXPAN). Based on this evaluation, an International Fragrance Association (IFRA) Standard has been established. The IFRA Standard restricts the use of citral in fragrances because of potential sensitization and recommends that citral only be used in association with substances that prevent a sensitizing effect.
Even though citral is a natural ingredient that is derived from plant sources, it can still lead to potentially serious allergic reactions. Symptoms of an allergic reaction to citral may include rashes, blisters, itchy skin, and swollen eyes and lips. In an article published by Today, Dr. Bruce Brod, a clinical professor of dermatology at the University of Pennsylvania, said, “I think it’s important for the public to be aware that just because something is all natural, it doesn’t mean it doesn’t cause side effects.”
Due to the possibility of an allergic reaction, those with sensitive skin should try to avoid citral or perform a patch test with any product containing this ingredient.
References for this information: Wikipedia, “Citral”, Lett Appl Microbiol. 1989, 9: 105-108, Evid Based Complement Alternat Med. 2017; 2017: 2505610, J Pathol. 2008 Jan;214(2):149-60.