All about Geraniol
Definition and origin of Geraniol
To fully understand what Geraniol, also called rhodinol, is, you have to delve into chemistry.
Citral, or lemonal, is the name given to two isomers with the chemical formula C10H16O. Both components are stereoisomers: the trans isomer is known as geranial or citral A. The cis isomer is known as neral or citral B.
Citral is the major constituent of lemongrass oil and other plants of the genus Cymbopogon. It is also present in the essential oils of verbena, orange, lemon...
Geraniol is the alcohol corresponding to Geranial. It is part of the family of monoterpene alcohols (alcohols very similar to those of phenols without having the disadvantages of the latter).
It is obtained by fractional distillation from the Cympobogon Winterianus Jowitt extracting all the impurities without any chemical means.
Geraniol comes in the form of a colorless liquid and gives off a pleasant smell of rose.
Geraniol is naturally present in many fruits, vegetables, spices and essential oils. For example, geraniol can be found in acacia oil, apple juice, beer, bergamot, coriander, ginger, nutmeg and thyme, blackberry, blueberry, rosewood, carrot, grapefruit juice, grapes, jasmine, lavender, lemon juice, lily of the valley, … and even certain aromatic grape varieties such as muscat or gewurztraminer which gives a perfumed wine with the smell of roses.
Chemical and physical properties of Geraniol
Family : monoterpene alcohols
IUPAC name : (2E)-3,7-dimethylocta-2,6-dien-1-ol
Molecular formula : C10H18O
Molar mass : 154.2493 ± 0.0096 g/mol
Density : 0.8894 g cm-3
Boiling temperature : 229°C
Biological properties of Geraniol
- Bactericidal activity
- Fungicidal activity
- Virucidal activity
- Immunomodulating activity
- Neurotonic or sedative activity
- Spasmolytic activity
Fields of application of Geraniol
Thanks to its floral smell (rose) and its special properties, geraniol is widely used by :
- The cosmetic industry (lip sticks, brilliantines, toothpastes, toilet waters, foundations, hair lacquers, aftershave lotions, hair lotions, perfumes, soaps, aerosols),
- The pharmaceutical industry : numerous specialties for topical use (contact lens cleaners, lozenges, ointments, suppositories (essences of citronella, essence of geranium, essence of lavender, essence of rose, etc.)
- Food industry : mostly as a flavoring agent (cloves, caramels, chewing gum, ice creams, sweets, liqueurs, cinnamon pastries). Geraniol is a product considered by the World Health Organization (WHO) as a food additive without particular danger.
- The detergent industry (household products, aerosols)
- It is also found in the manufacture of cigarettes (additive to improve the flavor – geraniol can also be found in its natural state in certain well-matured tobacco!), in industrial oils and fats, aromatic essences used in bakery, etc.
- Latest application : Geraniol in aqueous solution acts in two ways on insects, whatever the stage of metamorphosis (egg, larva, adult): by suffocation and by dehydration by acting on chitin (the protective envelope of the insect ). Geraniol is one of the best larvicide and ovicide on the market. It is therefore a product used naturally for the preventive control of fleas or ticks in domestic animals or to reinforce the insecticidal action of a product or even used as a repellent against hematophagous insects (feeding on blood), in the form of protection bracelet which one clings to the wrist.
Geraniol : effective protection against insects
This alcohol concentrates the insect repellent properties of geraniums, pelargoniums and other geraniaceae and acts as a formidable insect repellent (mites, mosquitoes, flies, ants, ticks, moths, etc.)
Although it drives away mosquitoes, flies, cockroaches, ants and ticks, there is this paradox which is the following: bees produce geraniol and use it to help them mark nectar flowers and locate the entrance to their hives.
As we saw above, geraniol has a significant effect on insects. This alcohol acts directly on the insect's cuticle (chitin) by suffocating and dehydrating it. Additionally, when used in sublethal doses, geraniol and monoterpenes are known to excite insect receptors by disrupting the host's olfactory profile, thereby helping to repel them.
Laboratory studies have found that the application of geraniol to the food substrate on which the insect feeds resulted both in a very significant reduction in the number of eggs laid on this substrate and also in observing an ovicidal activity. This substance therefore has a strong influence on the laying of adult insects. Our anti-larvae and anti-mosquito concentrate based on geraniol has also shown excellent results on insecticidal and ovicidal properties.
It will be understood, in addition to acting as a repellent, this substance therefore also acts as an insecticide (destruction of the insect). Despite everything, the Biocide Regulation 528/2012 (which aims to regulate the placing on the European market of biocidal products including insecticides and repellents) classifies geraniol in TP19: Repellent; and not in TP18: Insecticide.
Its CAS number (registration number of a chemical substance, polymer, biological sequence and alloy) is the following CAS n°106-24-1
In the United States, its toxicological profile allows it to be considered a low-risk pesticide.
Geraniol remains to this day an interesting alternative in terms of toxicology with respect to traditional insecticide substances.
Geraniol, an allergenic fragrance substance
The fact that people have allergic reactions to natural materials is well known. There are women and men who can't stand hazelnuts and cinnamon or who get hay fever from pollen. And since a large number of consumers are allergic to odorous substances, some of them or rather their components must be declared.
Contact allergies to cosmetic products are very common (2% of the European population is affected) and can cause eczema, among other things. In 45% of cases, these allergies are due to the fragrance substances contained in the cosmetic product (then 21% with preservatives with 21% and 10% with emulsifiers).
Previously, all fragrant substances were collected under the generic name Parfum (Fragrance).
Following Directive 2003/15/EC, since March 11, 2005, 26 substances, having, among other things, fragrant or aromatic properties, identified as being potentially allergenic, must appear clearly in the list of ingredients, regardless of their function, as soon as their concentration exceeds 0.001% in leave-in products (creams, etc.) and 0.01% in rinse-out products (shampoos, etc.).
Geraniol is included on this list as minimal allergenic potential.
The INCI declaration (international nomenclature of cosmetic ingredients) does not make it possible to know whether a cosmetics manufacturer has used a synthetic substance, a natural essential oil or an isolated component of the latter since the former have the same INCI name as the latter. This is why geraniol is found in many cosmetic products on the INCI list of ingredients.
Natural geraniol or synthetic geraniol ?
The difference can be decisive for allergy sufferers because there are clear indications proving that natural oils and synthetic substances cannot be judged in the same way.
The BDIH (the German interprofession) commissioned a study on geraniol. 50 people who reacted positively during an allergy test to geraniol were tested. The study focused on the reaction to geraniol contained in essential oils.
- 10 of these 50 people (20%) had a reaction to the chemically isolated fragrant substance geraniol.
- No one reacted to essential oils containing geraniol.
Allergic reactions due to perfumes is a priority for companies like Wala (Dr. Hauschka), which specializes in the manufacture of natural cosmetics. It also commissioned a study on Geraniol.
25 people with a contact allergy to the “fragrance mix” were tested (in a university dermatological clinic). The experimental protocol provided for a total of 500 tests using Dr. Hauschka oil.
- There were only 17 allergic reactions out of the 500 tests. However, we could have expected a higher number, the people tested being all “confirmed” allergic people.
- No allergic reaction for a concentration of 0.5%.
- 17 reactions in the form of contact allergy only in the case of a concentration of 5%. But you should know that in cosmetics, essential oils are generally present at 0.5 to 1%. A dosage of 5% is therefore well above normal.
The consumer cannot identify by reading the designations alone whether one of the fragrant substances is a synthetic substance or a component of a natural essential oil. Geraniol can be the component of an entirely natural product, an essential oil for example. On the other hand, geraniol can also be obtained from mineral oil or completely synthesized (synthetic chemistry).
It can be of essential importance for the consumer to know if the odorous substance is chemical or the component of a natural oil. In conclusion, prefer natural geraniol (plant extract) to synthesized geraniol.
Studies carried out on the repellency of geraniol against insects
Muller, G.C. et al. 2009). Effectiveness of geraniol, linalool and citronella as botanical mosquito repellents.
The authors concluded that geraniol exhibited significantly greater repellent activity than citronella or linalool against 4 mosquito species, both indoors and outdoors. Under identical experimental conditions, all the substances repelled more mosquitoes than in the absence of protection. Also, the repellents tested were more active in the continuous-release diffuser form than in the candle form.
Muller, G.C. et al. (2008a). Indoor protection against mosquito and sandfly bites : comparison of citronella, linalool and geraniol candles.
The authors conclude that geraniol is a more effective repellent against sandflies and mosquitoes than linalool or citronella. They also concluded that 5% of geraniol candles used indoors better met the repellency criteria presented by the EPA (Environmental Protection Agency). The geraniol candle offers superior protection compared to the other two essential oil candles tested.
Zhu, J.J., et al. (2015). Comparisons in terms of anti-appetance and spatial repellency of three natural repellents against the horn flies Haematobia irritans (Diptera: Muscidae).
The authors determined that the three natural repellents were effective in repelling horn flies, in terms of both anti-appetance (contact repellent) and spatial repellency. This study proposes an interesting strategy based on geraniol, which develops a push-pull relationship between a suitable repellent (geraniol) and a horn fly trap with bait, which can be used on cattle in the field. No SPME strategy was used in conjunction with laboratory testing. Therefore, there is no explanation for the higher rate of volatility of geraniol in the field.
Scientists have also determined that the density of repelled insects must be taken into account in order to determine the concentration of geraniol in a product and the reapplication time to indicate on a product label (Goodyer 2010; Pavela 2016). Is the product used in environments where the incidence of pitting is low or high? In environments where the incidence of biting is high, a higher concentration of geraniol may be recommended.
Finally, the use of geraniol as a single active ingredient rather than in combination with other compounds may be an efficiency factor. According to a study, the geraniol present in essential oils used in synergy with other components explains the high performance of lemongrass essential oil, compared to the use of geraniol alone (Deletre et al. 2016). Nevertheless, other studies have demonstrated that the repellency of geraniol used as the sole active ingredient is greater than that of lemongrass (Müller et al. 2008a; Müller et al. 2008b).
It should therefore be left to each manufacturer of insecticides and repellents to test and use geraniol alone, or in combination with other components.