What is an oil macerate?

An oil macerate is the product of the maceration process of aromatic plant parts (flowers, leaves, roots, buds, young shoots, etc.) in a neutral vegetable oil, which then acts as a carrier/solvent for the active properties of the plant. Indeed, the liposoluble active substances contained in the plant (essential fatty acids, vitamins, esters, alcohols, etc.) are transferred to the vegetable oil.

The term "macerate" can also refer to a extract obtained by macerating natural elements in a mixture of water, ethyl alcohol and glycerine in order to extract the water-soluble active ingredients, such as tannins, phenols, certain vitamins, mineral salts, alkaloids and most flavonoids: we then speak of a glycerine macerate.

What are the properties?

Depending on the plant and the part of the plant selected, oil macerates can contain various actions, brought about by the different molecules that compose them, in addition to those of the carrier oil. Thus, they can be nourishing, softening, sebum-regulating, toning, healing... Moreover, it penetrates very quickly into the epidermis, which allows for the reconstitution of the skin's hydrolipidic film through a composition rich in essential fatty acids.

How to use it?

The oil macerate is applied at the end of the routine after the moisturising cream, due to its oily texture. It can be used alone or in combination with others. A significant advantage of opting for oil macerates is that they can be a good alternative to essential oil, given that the latter has usage restrictions and therefore requires greater precautions, particularly in pregnant or breastfeeding women, and children. Indeed, an oil macerate provides the same benefits but with fewer harmful effects.

Why resort to maceration?

The "maceration" option is preferred when it is challenging to produce oil from the selected plant, even though it possesses intriguing properties. Indeed, the vegetable oil is a fatty substance extracted from an oilseed plant, that is, a plant whose seeds, nuts, or fruits contain fatty acids.

Be mindful of the terminology used. Some "oil macerates" may be referred to as "vegetable oil".

Maceration is an extraction technique that involves "infusing" a part of an aromatic plant in a neutral vegetable oil for a defined period, here are the steps:

1. Preparing the plant: An oil macerate is typically obtained from dried plants, particularly for parts rich in water such as bulbs, fruits, roots... Indeed, this step prevents the water contained in the fresh plant from spoiling the macerate due to the risk of fermentation. Of course, choosing between a dried or fresh plant also depends on the extraction process used. If the maceration is done hot, using a fresh plant is not a problem. In other cases, the plant is sometimes ground into powder before being left to macerate;

   Information : Some plants may lose their properties if they are dried, such as lemon balm, St John's wort, etc...

2. Selecting the maceration oil: The type olive oil, of sunflower, grape seed, argan, etc... the oil used should be selected based on its intrinsic properties, that is, its composition in fatty acids or unsaponifiables. It is recommended to choose a mono-unsaturated oil, with good stability at room temperature, and a low oxidation potential, thus ensuring long-term use of the macerate. Of plant origin, this carrier oil should preferably be obtained by first cold pressing for better preservation of thermolabile compounds (vitamins, antioxidants, etc...) and having undergone no treatment before or after pressing: it is then qualified as virgin oil;

• Hot Maceration: This technique involves heating the "oil + plant" mixture in an oven, in an inert atmosphere to prevent oxidation, in order to accelerate the release of active ingredients. The downside? Although it only requires a few hours of maceration, this method nevertheless carries the risk of altering certain active ingredients such as vitamins, flavonoids... which are sensitive to high temperatures;

• Cold Maceration: The absence of temperature elevation allows the preservation of the integrity of thermolabile chemical species (vitamins, flavonoids...), and thus their properties. It is carried out at room temperature or in the sun to utilise its heat (solar maceration); however, the mixture must be protected from UV rays which can promote the oxidation of the vegetable oil or alter the active components of the plant. The downside? This maceration process requires a longer impregnation duration of the plant extract by the fatty substance (between 3 and 4 weeks).

In the cosmetics industry, the oil macerate is obtained by simple pressing of plant extracts to extract the liposoluble active ingredients.

Sometimes, preservatives, such as Vitamin E (INCI name: Tocopherol), or even an essential oil like rosemary essential oil, are added at the end of the procedure to keep the mixture as long as possible.

Here are some examples of macerates, the most well-known and widely used in the cosmetics industry:

• The arnica macerate (INCI name: Arnica Montana Flower Extract) is recognised for its anti-inflammatory and healing virtues due to its content of sesquiterpene lactones (helenalin, arnifolin, etc...). It thus helps to alleviate various ailments (sunburn, superficial burns, shocks, insect bites, etc...). Its circulatory effect makes it an ideal ingredient to prevent blood accumulation and therefore reduce the formation of oedemas or bruises. It also serves as a good base for massage oil, appreciated for relaxing muscles after a workout and preventing muscle soreness or for treating a painful joint, or in prevention of intense muscular activity. This practice also helps to alleviate heavy legs. The oily arnica macerate also has antioxidant properties conferred by its content of omega-6 and 9 and polyphenols, thus protecting the skin from premature ageing. Moreover, its high carotenoid content lends it a photoprotective role.

  Any contraindications? Do not use on open wounds.

• The calendula macerate (INCI name: Calendula Officinalis Flower Extract) is particularly suitable for individuals with sensitive, irritated skin prone to discomfort. It is primarily anti-inflammatory and antioxidant, with additional soothing, nourishing, healing, and photoprotective properties. Indeed, its high content of faradiol esters allows it to act on all types of skin inflammation, in connection with its soothing action. Moreover, it also limits the appearance of signs of ageing with its antioxidant virtues thanks to its high level of carotenoids (beta-carotene, flavoxanthin, lutein, lycopene, etc...) and flavonoids (quercetin, lupeol, etc...). Indeed, it fights against free radicals, responsible for cellular degeneration. Furthermore, thanks to the presence of flavonoids and faradiol, the calendula oil macerate accelerates the regeneration of skin cells. Finally, due to its high oleic acid content, it also has nourishing properties, thus allowing it to hydrate the layers of the skin, and restore its suppleness and elasticity.

  Any contraindications? If you have an allergy to Asteraceae, it is advisable as a precautionary principle not to use it.

• The carrot oil macerate (INCI name: Daucus Carota Sativa Root Extract) is known for providing a "healthy glow" effect and thus being an ally for dull and tired skin. Thanks to the lutein and beta-carotenes (provitamin A), a colouring substance it contains, it gives a slight natural "tanned" hue to the skin, thereby reviving dull complexions. Beta-carotene also has the ability to stimulate melanin synthesis. Its high content of antioxidant actives (beta-carotene, xanthine derivatives, lutein...) also allows it to protect the epidermis against daily aggressions, due to their antioxidant properties: it will capture the free radicals produced by sun exposure and thus fight against the effects of ageing. Furthermore, it is appreciated by people with dry and frizzy hair due to its nourishing properties with its high content of linoleic and oleic acid. This also helps to strengthen the skin's hydrolipidic film, thus preventing dehydration.

  Any contraindications? There are no contraindications to the cosmetic use of carrot macerate.

• The St. John's Wort macerate (INCI name: Hypericum Perforatum Oil) soothes, repairs and heals damaged and stressed skin (burns, sunburn, dermatitis, baby diaper rash...). Indeed, it contributes to skin regeneration by stimulating the synthesis of collagen by fibroblasts, an action conferred by the phytosterols (hypericin, hyperforin) it contains. Its content of hypericin, hyperforin and sesquiterpene terpenes also allows it to limit the extent of inflammatory reactions. The St. John's Wort macerate also proves to be antibacterial due to the presence of hyperforin. Finally, this macerate is rich in omega-9 (oleic acid), helping to maintain skin hydration.

  Any contraindications?This oil macerate contains photosensitising molecules (hypericin and its derivatives), meaning that exposure to the sun is strongly advised against following its application, under the risk of developing brown spots.

• DE WITTE P. A. & al. Skin photosensitization with topical hypericin in hairless mice. Journal of Photochemistry and Photobiology B: Biology (1999).

• MERFORT I & al. Skin penetration studies of Arnica preparations and of their sesquiterpene lactones. Planta Medica (2004).

• TASDEMIR D. & al. Assessment of antimicrobial and antiprotozoal activity of the olive oil macerate samples of Hypericum perforatum and their LC–DAD–MS analyses. Food Chemistry (2013).

• CASADO J. & al. Anthocyanin profile and antioxidant capacity of black carrots (Daucus carota L. ssp. sativus var. atrorubens Alef.) from Cuevas Bajas, Spain. Journal of Food Composition and Analysis  (2014).

• PAVLOV A. Plant Cell culture as emerging technology for production of active cosmetic ingredients. Engineering in Life Sciences (2018).

• SOUZA L. C. & al. Anti-inflammatory effect of Arnica montana in a UVB radiation-induced skin-burn model in mice. Cutaneous and Ocular Toxicology (2020).

• YU L. & al. Triacylglycerols and fatty acid compositions of cucumber, tomato, pumpkin, and carrot seed oils by ultra-performance convergence chromatography combined with quadrupole time-of-flight mass spectrometry. Foods (2020).