Lipids for Cosmetic Applications

Fatty acids from vegetable oils are commonly used in cosmetic formulations, with unsaturated fatty acids found in triglycerides offering the most beneficial cosmetic properties. Various oils, fats, waxes, and phospholipids are utilized as lipid excipients in cosmetics and personal care items. Antioxidants like carotenoids, retinoids, and tocopherols are crucial in therapeutic care for their antioxidant qualities. Linoleic acid and alpha-linolenic acid-rich oils are key for skin care, aiding in reducing eczema and atopic dermatitis by integrating into cell membranes, regenerating damaged lipid barriers, and preventing water loss. These unsaturated fatty acids are effective in treating skin inflammation and are commonly used in cosmetics.

What are Lipids?

Lipids represent a diverse and distinctive group of natural organic compounds present in plants, animals, and microorganisms. They constitute one of the primary food groups alongside proteins and carbohydrates that animals consume. These natural compounds encompass fatty acids and their derivatives, playing crucial roles in the structure and metabolism of all living organisms. Serving as vital components of cell membrane structure (such as phospholipids and cholesterol derivatives), lipids act as significant sources and reserves of energy (specifically triglycerides). Their efficiency in storage surpasses that of carbohydrates due to the highly reduced state of their carbon chains, maximizing energy release upon digestion and oxidation into carbon dioxide and water. Being hydrophobic with long hydrocarbon chains, lipids are sometimes amphiphilic, featuring hydrophilic domains like phosphates, glycerol, nitrogen, and alcohols. While insoluble in water, they dissolve in organic solvents. Complex polar lipids exhibit non-lipid chemical groups like phosphates and carbohydrate moieties, making them valuable components in cosmetic formulations due to their amphiphilic properties. These complex lipids can be categorized as neutral lipids and polar lipids based on their polarity, with the latter comprising lipids with a phosphate moiety (known as phospholipids) and glycolipids containing glucose.

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What Lipids are Used in Cosmetics?

The two main functions of the stratum corneum (SC) are to prevent excessive water loss and to prevent xenobiotics from penetrating into the dermis to avoid immune reactions. The main components of SC are keratinocytes and intercellular lipids, which are contained in an envelope of highly cross-linked proteins (loricrin, involucrin, filaggrin). The optimal water gradient is maintained by keratinocyte lipids and NMF, which are responsible for maintaining adequate hydration of the SC. Most of the lipids that make up SC are ceramide, cholesterol and fatty acids, and a small amount of components are phospholipids and cholesterol sulfate. The PC fraction in soybean oil helps improve skin moisture and emollient properties; phosphatidyl lecithin also provides softening properties in creams, lotions and shampoos. In addition to their known functional applications as surfactants or emulsifiers, polar lipids play an important role in various physiological functions to keep skin healthy and disease-free.

Fig. 1. Dermatopathology of lipid cosmeceuticals (Biomed Dermatol. 2020, 4: 12).

What is the Application of Lipid in Cosmetic Industry?

Lipids found in cosmetics are designed for application on the skin to protect and enhance the body's appearance, create a protective shield against external pollutants, and maintain skin hydration and flexibility. Fatty acids commonly used in cosmetic products are blends of triglycerides composed of both saturated and unsaturated fatty acids, forming esters of glycerol and higher fatty acids with an even number of aliphatic carbon atoms. In cosmetic emulsions, which are prevalent in personal care items, key components include lipids such as vegetable oils and fatty acids, as well as their derivatives like emollients and emulsifiers.

Liposomes

Liposomes, small artificial spherical vesicles that can be made from a variety of positively and negatively charged amphipathic molecules, including cholesterol and natural phospholipids, which determine their rigidity or fluidity, are promising drug delivery carriers. Liposome membranes are usually composed of synthetic or natural phospholipids, in which the incorporation of cholesterol enhances stability. Therefore, the physicochemical properties of liposomes are mainly modulated by the incorporated phospholipids. Lecithin is the main phospholipid used in liposomes and is either derived from natural sources such as eggs and soybeans or has synthetic characteristics. They may be particularly promising as intracellular delivery agents for ribosomes, proteins or peptides, and DNA. Liposomes are widely used as molecular carriers in the cosmetic and pharmaceutical industries for delivery systems that capture unstable compounds such as antibiotics, antioxidants, and biomolecules. They can surround hydrophobic and hydrophilic compounds, preventing the captured molecules from breaking down and releasing them to their designated targets. Unsaturated phosphatidylcholine (PC) (egg or soybean phosphatidylcholine) forms a fairly permeable and unstable bilayer, while saturated phospholipids with acyl chains (dipalmitoyl phosphatidylcholine) form a more rigid and impermeable structure. Other important applications of liposomal cosmetic formulations include anti-aging, antioxidants, activators, stimulation of skin collagen production and anti-inflammatory agents.

Lipid Nanoparticles

In recent years, numerous studies have been conducted to describe the use of lipid-based materials in topical applications. These materials include, but are not limited to, emulsions, microemulsions, multiple emulsions, etc. Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) are nanoparticles composed of solid lipids or solid lipid mixtures, respectively. Among them, solid lipid nanoparticles first entered the market and are therefore called first-generation lipid nanoparticles, followed by improved second-generation nanoparticles, namely nanostructured lipid carriers. These nanoparticles are commonly used as nanocarriers for pharmaceutically active agents such as drugs, inhibitors, and other pharmaceutical or cosmeceuticals. They are synthesized and formulated through high-pressure homogenization, and their shape, size, and surface morphology are characterized by various techniques such as transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. They combine various properties of traditional nanocarriers, such as chemical stability, good skin compatibility, and are used for UV and IR radiation protection in anti-aging products. For example, as cosmeceutical formulations, silver nanolipid (sNLC) complexes are effective in skin care to treat atopic dermatitis and psoriasis.

Fig. 2. Lipid nanoparticles for cosmeceutical products (Biomed Dermatol. 2020, 4: 12).

Essential Oils and Mineral Oils

Essential oils and their compounds are widely used in cosmetics because of their numerous benefits, including their pleasant aroma. Their useful biological activities include pathophysiological activities such as analgesic, antiseptic, antibacterial, carminative, diuretic, antispasmodic, hyperemic and stimulant properties. Due to the antibacterial and antifungal properties of essential oils, chemical preservatives are generally not required if PCP contains essential oils as active ingredients (e.g. rosemary oil, eucalyptus oil). Essential oils are usually composed of lipophilic small molecules and non-polar molecules, such as terpenes, rosemary oil, etc.

Wax

Wax is created by combining hard and brittle substances, high molecular weight monoalcohols with fatty acid esters. Waxes are present in both plants and animals, including marine life. They play a crucial role in reducing water loss in plants and serving as water repellents for animals. Jojoba seed and sperm whale oil liquid waxes (esters) are utilized in various commercial applications such as lubricants, wax polishes, and additives in cosmetics. Lanolin, a type of wax, is derived from sheep's sebaceous secretions (wool fat) and consists of a complex mixture of fatty acid esters and high molecular weight aliphatic and steroid alcohols. Sebum, an oily waxy substance secreted by sebaceous glands, protects and moisturizes the skin and hair. Sebum is versatile and is used as a binder, stabilizer, and conditioner in products like lipsticks, cosmetics, eye products, creams, and lotions. This odorless and tasteless wax is soluble in mineral oil and can be incorporated into bath oil products.

In Conclusion

There is a large and growing demand for active, natural, safe cosmetic ingredients, including lipids. Many oils, fats, waxes and phospholipids are used as excipients in cosmetics and PCP formulations. Antioxidants such as carotenoids, retinoids, and tocopherols play an important role in therapeutic care due to their antioxidant properties. Additionally, lipid nanoparticles can be used to protect against harmful radiation and as anti-aging compounds. As cosmeceutical preparations, nanoformulations are effective against irritated and inflamed skin and are effective in the treatment of atopic dermatitis and psoriasis.

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Reference

1. Ahmad, A. et al. Lipid-based formulations in cosmeceuticals and biopharmaceuticals. Biomed Dermatol. 2020, 4: 12.